diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
index 0000000..375d10a
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,236 @@
+name: CI
+
+on: [push, pull_request]
+
+env:
+  BUILD_DIR: _build
+  PIP_PACKAGES: >-
+    meson==0.58.0
+    cmake
+    ninja
+    gcovr
+  MACOS_BASEKIT_URL: >-
+    https://registrationcenter-download.intel.com/akdlm/irc_nas/17969/m_BaseKit_p_2021.3.0.3043.dmg
+  MACOS_HPCKIT_URL: >-
+    https://registrationcenter-download.intel.com/akdlm/irc_nas/17890/m_HPCKit_p_2021.3.0.3226_offline.dmg
+  LINUX_INTEL_COMPONENTS: >-
+    intel-oneapi-compiler-fortran
+    intel-oneapi-compiler-dpcpp-cpp-and-cpp-classic
+    intel-oneapi-mkl
+    intel-oneapi-mkl-devel
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest]
+        build: [meson]
+        build-type: [debug]
+        compiler: [intel]
+        version: [2021]
+
+        include:
+          - os: ubuntu-latest
+            build: meson
+            build-type: debug
+            compiler: gnu
+            version: 11
+
+          - os: ubuntu-latest
+            build: meson
+            build-type: debug
+            compiler: gnu
+            version: 9
+
+    env:
+      FC: ${{ matrix.compiler == 'intel' && 'ifort' || 'gfortran' }}
+      CC: ${{ matrix.compiler == 'intel' && 'icc' || 'gcc' }}
+      GCC_V: ${{ matrix.version }}
+      OMP_NUM_THREADS: 1,2,1
+      PYTHON_V: 3.8
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v2
+
+    - uses: actions/setup-python@v1
+      with:
+        python-version: ${{ env.PYTHON_V }}
+
+    - name: Install GCC (OSX)
+      if: ${{ contains(matrix.os, 'macos') && matrix.compiler == 'gnu' }}
+      run: |
+          brew install gcc@${{ env.GCC_V }}
+          ln -s /usr/local/bin/gfortran-${GCC_V} /usr/local/bin/gfortran
+          which gfortran-${GCC_V}
+          which gfortran
+
+    - name: Install GCC (Linux)
+      if: ${{ contains(matrix.os, 'ubuntu') && matrix.compiler == 'gnu' }}
+      run: |
+        sudo add-apt-repository ppa:ubuntu-toolchain-r/test
+        sudo apt-get update
+        sudo apt-get install -y gcc-${{ env.GCC_V}} gfortran-${{ env.GCC_V }}
+        sudo update-alternatives \
+        --install /usr/bin/gcc gcc /usr/bin/gcc-${{ env.GCC_V }} 100 \
+        --slave /usr/bin/gfortran gfortran /usr/bin/gfortran-${{ env.GCC_V }} \
+        --slave /usr/bin/gcov gcov /usr/bin/gcov-${{ env.GCC_V }}
+
+    - name: Install GCC (Windows)
+      if: ${{ contains(matrix.os, 'windows') && matrix.compiler == 'gnu' }}
+      uses: msys2/setup-msys2@v2
+      with:
+        msystem: MINGW64
+        update: false
+        install: >-
+          git
+          mingw-w64-x86_64-gcc-fortran
+          mingw-w64-x86_64-openblas
+          mingw-w64-x86_64-lapack
+          mingw-w64-x86_64-cmake
+          mingw-w64-x86_64-meson
+          mingw-w64-x86_64-ninja
+
+    - name: Prepare for cache restore
+      if: ${{ matrix.compiler == 'intel' }}
+      run: |
+        sudo mkdir -p /opt/intel
+        sudo chown $USER /opt/intel
+
+    - name: Cache Intel install
+      if: ${{ matrix.compiler == 'intel' }}
+      id: cache-install
+      uses: actions/cache@v2
+      with:
+        path: /opt/intel/oneapi
+        key: install-${{ matrix.compiler }}-${{ matrix.version }}-${{ matrix.os }}
+
+    - name: Install Intel (Linux)
+      if: ${{ contains(matrix.os, 'ubuntu') && contains(matrix.compiler, 'intel') && steps.cache-install.outputs.cache-hit != 'true' }}
+      run: |
+        wget https://apt.repos.intel.com/intel-gpg-keys/${{ env.KEY }}
+        sudo apt-key add ${{ env.KEY }}
+        rm ${{ env.KEY }}
+        echo "deb https://apt.repos.intel.com/oneapi all main" | sudo tee /etc/apt/sources.list.d/oneAPI.list
+        sudo apt-get update
+        sudo apt-get install ${{ env.PKG }}
+      env:
+        KEY: GPG-PUB-KEY-INTEL-SW-PRODUCTS-2023.PUB
+        PKG: ${{ env.LINUX_INTEL_COMPONENTS }}
+
+    - name: Install Intel BaseKit (OSX)
+      if: ${{ contains(matrix.os, 'macos') && contains(matrix.compiler, 'intel') && steps.cache-install.outputs.cache-hit != 'true' }}
+      run: |
+        curl --output ${{ env.OUT }} --url "$URL" --retry 5 --retry-delay 5
+        hdiutil attach ${{ env.OUT }}
+        if [ -z "$COMPONENTS" ]; then
+          sudo /Volumes/"$(basename "$URL" .dmg)"/bootstrapper.app/Contents/MacOS/bootstrapper -s --action install --eula=accept --continue-with-optional-error=yes --log-dir=.
+          installer_exit_code=$?
+        else
+          sudo /Volumes/"$(basename "$URL" .dmg)"/bootstrapper.app/Contents/MacOS/bootstrapper -s --action install --components="$COMPONENTS" --eula=accept --continue-with-optional-error=yes --log-dir=.
+          installer_exit_code=$?
+        fi
+        hdiutil detach /Volumes/"$(basename "$URL" .dmg)" -quiet
+        exit $installer_exit_code
+      env:
+        OUT: webimage-base.dmg
+        URL: ${{ env.MACOS_BASEKIT_URL }}
+        COMPONENTS: intel.oneapi.mac.mkl.devel
+
+    - name: Install Intel HPCKit (OSX)
+      if: ${{ contains(matrix.os, 'macos') && contains(matrix.compiler, 'intel') && steps.cache-install.outputs.cache-hit != 'true' }}
+      run: |
+        curl --output ${{ env.OUT }} --url "$URL" --retry 5 --retry-delay 5
+        hdiutil attach ${{ env.OUT }}
+        if [ -z "$COMPONENTS" ]; then
+          sudo /Volumes/"$(basename "$URL" .dmg)"/bootstrapper.app/Contents/MacOS/bootstrapper -s --action install --eula=accept --continue-with-optional-error=yes --log-dir=.
+          installer_exit_code=$?
+        else
+          sudo /Volumes/"$(basename "$URL" .dmg)"/bootstrapper.app/Contents/MacOS/bootstrapper -s --action install --components="$COMPONENTS" --eula=accept --continue-with-optional-error=yes --log-dir=.
+          installer_exit_code=$?
+        fi
+        hdiutil detach /Volumes/"$(basename "$URL" .dmg)" -quiet
+        exit $installer_exit_code
+      env:
+        OUT: webimage-hpc.dmg
+        URL: ${{ env.MACOS_HPCKIT_URL }}
+        COMPONENTS: all
+
+    - name: Setup Intel oneAPI environment
+      if: ${{ matrix.compiler == 'intel' }}
+      run: |
+        source /opt/intel/oneapi/setvars.sh
+        printenv >> $GITHUB_ENV
+
+    - name: Install build and test dependencies
+      if: ${{ ! contains(matrix.os, 'windows') }}
+      run: pip3 install ${{ env.PIP_PACKAGES }} ${{ env.PIP_EXTRAS }}
+
+    - name: Configure build (meson)
+      if: ${{ matrix.build == 'meson' }}
+      run: >-
+        meson setup ${{ env.BUILD_DIR }}
+        --buildtype=debug
+        --prefix=$PWD/_dist
+        --libdir=lib
+        --warnlevel=0
+        -Db_coverage=${{ env.COVERAGE }}
+        ${{ env.MESON_ARGS }}
+      env:
+        COVERAGE: ${{ matrix.build-type == 'coverage' }}
+        MESON_ARGS: ${{ matrix.compiler == 'intel' && '-Dfortran_link_args=-qopenmp' || '' }}
+
+    - name: Configure build (CMake)
+      if: ${{ matrix.build == 'cmake' }}
+      run: >-
+        cmake -B${{ env.BUILD_DIR }}
+        -GNinja
+        -DCMAKE_BUILD_TYPE=Debug
+        -DCMAKE_INSTALL_PREFIX=$PWD/_dist
+        -DCMAKE_INSTALL_LIBDIR=lib
+
+    - name: Build library
+      run: ninja -C ${{ env.BUILD_DIR }}
+
+    - name: Run unit tests
+      if: ${{ matrix.build == 'meson' }}
+      run: |
+         meson test -C ${{ env.BUILD_DIR }} --print-errorlogs --no-rebuild --num-processes 1 -t 2
+
+    - name: Run unit tests
+      if: ${{ matrix.build == 'cmake' }}
+      run: |
+         ctest --output-on-failure --parallel 2
+      working-directory: ${{ env.BUILD_DIR }}
+
+    - name: Create coverage report
+      if: ${{ matrix.build == 'meson' && matrix.build-type == 'coverage' }}
+      run:
+         ninja -C ${{ env.BUILD_DIR }} coverage
+
+    - name: Install project
+      run: |
+        ninja -C ${{ env.BUILD_DIR }} install
+        echo "PLOTMS_PREFIX=$PWD/_dist" >> $GITHUB_ENV
+
+    - name: Create package
+      if: ${{ matrix.build == 'meson' }}
+      run: |
+        tar cvf ${{ env.OUTPUT }} _dist
+        xz -T0 ${{ env.OUTPUT }}
+        echo "PLOTMS_OUTPUT=${{ env.OUTPUT }}.xz" >> $GITHUB_ENV
+      env:
+        OUTPUT: plotms-${{ matrix.compiler }}-${{ matrix.version }}-${{ matrix.os }}.tar
+
+    - name: Upload package
+      if: ${{ matrix.build == 'meson' && matrix.build-type != 'coverage' }}
+      uses: actions/upload-artifact@v2
+      with:
+        name: ${{ env.PLOTMS_OUTPUT }}
+        path: ${{ env.PLOTMS_OUTPUT }}
+
+    - name: Upload coverage report
+      if: ${{ matrix.build == 'meson' && matrix.build-type == 'coverage' }}
+      uses: codecov/codecov-action@v1
diff --git a/config/meson.build b/config/meson.build
new file mode 100644
index 0000000..5d69d65
--- /dev/null
+++ b/config/meson.build
@@ -0,0 +1,47 @@
+# This file is part of PlotMS.
+
+os = host_machine.system()
+fc = meson.get_compiler('fortran')
+fc_id = fc.get_id()
+static = get_option('default_library') == 'static' and get_option('fortran_link_args').contains('-static')
+
+#> choose compiler options
+if fc_id == 'gcc'
+  add_project_arguments(
+    '-ffree-line-length-none',
+    '-fbacktrace',
+    language: 'fortran',
+  )
+  if fc.version().version_compare('<8')
+    error('GCC version 8 or higher is required.')
+  endif
+elif fc_id == 'intel'
+  add_project_arguments(
+    '-traceback',
+    language: 'fortran',
+  )
+  add_project_arguments(
+    '-DLINUX',
+    language: 'c',
+  )                                                                                                                                                                                                                                                                    
+elif fc_id == 'pgi' or fc_id == 'nvidia_hpc'
+  add_project_arguments(
+    '-Mbackslash',
+    '-Mallocatable=03',
+    '-traceback',
+    language: 'fortran',
+  )
+  error('This project does not support compilation with NVHPC yet')
+endif
+########################################################################
+
+
+# Create the tool chain library as subproject
+mctc_dep = dependency(
+  'mctc-lib',
+  version: '>=0.2',
+  fallback: ['mctc-lib', 'mctc_dep'],
+  default_options: ['default_library=static'],
+  static: static,
+)
+exe_deps += mctc_dep
diff --git a/entries.f90 b/entries.f90
deleted file mode 100644
index 1961e2b..0000000
--- a/entries.f90
+++ /dev/null
@@ -1,165 +0,0 @@
-module count_entries
-  use xtb_mctc_accuracy, only: wp
-  implicit none
-
-  contains
-
-    subroutine check_entries(index_mass, isotope_masses, exact_intensity, &
-        list_masses,  intensity,  count_mass, chrg)
-   
-      integer :: loop, loop2, index_mass
-      integer :: count_mass
-      integer :: sum_index, i
-      integer :: check
-    
-      !real(wp) :: intensity(index_mass)
-      real(wp) :: xmass
-      real(wp) :: isotope_masses(index_mass)
-      real(wp) :: exact_intensity(index_mass)
-      real(wp) :: chrg
-
-      real(wp) :: list_masses(10000)
-      real(wp) :: intensity(10000)
-    
-      !real(wp), allocatable :: list_masses(:)
-      !real(wp), allocatable :: save_list(:)
-      !real(wp), allocatable :: save_int(:)
-      !real(wp), allocatable :: intensity(:)
-      !real (wp) :: save_list(1000)
-      !real (wp) :: save_list(1000)
-
-      logical :: there = .true.
-
-      xmass = 0
-      loop = 0
-      loop2 = 0
-      check = 0
-      !count_mass = count_mass + index_mass
-      if(count_mass == 0)then
-        sum_index =  index_mass
-      !  allocate ( list_masses(index_mass))
-      !  allocate ( intensity(index_mass))
-      else
-        sum_index = count_mass + index_mass
-      !  if(allocated(save_list)) write(*,*) 'JOP'
-      !  if(allocated(save_list))deallocate (save_list)
-      !  if(allocated(save_int))deallocate (save_int)
-      !  allocate ( save_list(count_mass))
-      !  allocate ( save_int (count_mass))
-
-      ! !write(*,*) 'COUNT MASS', count_mass
-      ! do i = 1, count_mass 
-      !  save_list(i) = list_masses(i)
-      !  save_int(i)  = intensity(i)
-      ! enddo
-
-      !  deallocate (list_masses)
-      !  deallocate (intensity)
-      !  allocate ( list_masses(sum_index))
-      !  allocate ( intensity(sum_index))
-
-      !   !write(*,*) 'save', save_list
-      !   !write(*,*) 'list', list_masses
-
-      !  do i = 1, count_mass
-      !    list_masses(i)  = save_list(i)
-      !    intensity(i)    = save_int(i)
-      !  enddo
-      endif
-
-
-      !if (.not. allocated(list_masses)) allocate ( list_masses(sum_index))
-
-      !write(*,*) 'BUCKET'
-      !write(*,*) 'index', index_mass
-      !write(*,*) 'sum', sum_index
-      !write(*,*) 'count', count_mass
-
-outer: do loop2 = 1, index_mass 
-        loop = 0
-        !write(*,*) isotope_masses(loop2)
-
-        !write(*,*) 'LOOP2', loop2
-        do 
-          loop = loop + 1
-
-          if  ( list_masses(loop) == isotope_masses(loop2) ) then
-          !write(*,*) 'LOOP', loop, 'TRUE'
-            there = .true.
-            !write(*,*) 'TRUE'
-            !write(*,*) 'intensity', loop,intensity(loop)
-            !intensity(loop) = intensity(loop) + 1
-            intensity(loop) = intensity(loop) +  1 * exact_intensity(loop2) &
-              * abs(chrg)
-            if (loop2 < index_mass ) cycle outer 
-            if (loop2 == index_mass ) exit 
-
-          elseif ( list_masses(loop) == 0.0_wp ) then
-            there = .false.
-             !write(*,*) 'NULL'
-            exit
-
-          !>> false if not in list, store
-          elseif ( list_masses(loop) /= isotope_masses(loop2) ) then
-          !write(*,*) 'LOOP', loop, 'FALSE'
-            there = .false.
-            !write(*,*) 'FALSE'
-            !write(*,*) loop, loop2
-            !if (loop == count_mass ) exit
-            if (loop == sum_index ) exit
-          endif
-        enddo
-
-
-        if ( .not. there ) then
-          count_mass = count_mass + 1
-          list_masses(count_mass) = isotope_masses(loop2)
-          intensity(count_mass) = intensity(count_mass) + 1 * exact_intensity(loop2) &
-            * abs(chrg)
-        endif
-
-      enddo outer
-
-      !if(allocated(intensity) .and. allocated(save_int)) then
-      !  deallocate (save_int)
-      !  allocate (save_int(count_mass))
-
-      !  do i = 1, count_mass 
-      !    save_int(i)=intensity(i)
-      !   enddo
-
-      !    deallocate (intensity)
-      !    allocate ( intensity(count_mass))
-
-      !    do i = 1, count_mass 
-      !      intensity(i)    = save_int(i)
-      !    enddo
-      !endif
-
-      !if(allocated(list_masses) .and. allocated(save_list)) then
-      !  deallocate (save_list)
-      !  allocate (save_list(count_mass))
-
-      !  do i = 1, count_mass 
-      !    save_list(i)=list_masses(i)
-      !   enddo
-
-      !    deallocate (list_masses)
-      !    allocate ( list_masses(count_mass))
-
-      !    do i = 1, count_mass 
-      !      list_masses(i)    = save_list(i)
-      !    enddo
-      !  write(*,*) 
-      !endif
-      !deallocate (save_list)
-      !deallocate (save_int)
-
-      !    do i = 1, count_mass 
-        !    write(*,*) i,list_masses(i),intensity(i)
-            !write(*,*) i,intensity(i)
-       !   enddo
-   
-    end subroutine check_entries
-    
-end module count_entries 
diff --git a/meson.build b/meson.build
index 585ff03..b0feb66 100644
--- a/meson.build
+++ b/meson.build
@@ -1,9 +1,9 @@
 # This build file is part of the PlotMS program 
 # for plotting QCxMS files
 
-project('PlotMS',
+project('plotms',
         'fortran',
-        version: '6.0',
+        version: '6.2',
         license: 'LGPL-3.0-or-later',
         meson_version: '>=0.55',
         default_options: [
@@ -11,19 +11,42 @@ project('PlotMS',
         'default_library=static',
   ],
 )
+install = not (meson.is_subproject() and get_option('default_library') == 'static')
 
-srcs = ['main.f90',
-       'isotopes.f90',
-       'boxmuller.f90',
-       'entries.f90',
-       'readcommon.f90',
-       'readl.f90',
-       'xtb_mctc_accuracy.f90',
-       'xtb_mctc_symbols.f90',
-       'xtb_mctc_resize.f90'
-       ]
+
+prog = []
+srcs = []
+exe_deps = []
+
+# Collect sources
+subdir('config')
+subdir('src')
 
 #plotms_exe = executable(
-executable('plotms',srcs)
+#executable('plotms',srcs)
+#
+# Create library target
+plotms_lib = library(
+  meson.project_name(),
+  sources: srcs,
+  dependencies: exe_deps,
+)
+
+# Export as dependency
+plotms_inc = plotms_lib.private_dir_include()
+plotms_dep = declare_dependency(
+  link_with: plotms_lib,
+  include_directories: plotms_inc,
+  dependencies: exe_deps,
+)
+
+
+# Create executable target
+plotms_exe = executable(
+  meson.project_name(),
+  sources: prog,
+  dependencies: plotms_dep,
+  install: install,
+)
 
 
diff --git a/boxmuller.f90 b/src/boxmuller.f90
similarity index 100%
rename from boxmuller.f90
rename to src/boxmuller.f90
diff --git a/src/entries.f90 b/src/entries.f90
new file mode 100644
index 0000000..7dd1927
--- /dev/null
+++ b/src/entries.f90
@@ -0,0 +1,91 @@
+module count_entries
+  use xtb_mctc_accuracy, only: wp
+  implicit none
+
+  contains
+
+    subroutine check_entries(index_mass, isotope_masses, exact_intensity, &
+        list_masses,  intensity,  count_mass, chrg)
+   
+      integer :: loop, loop2, index_mass
+      integer :: count_mass
+      integer :: sum_index, i
+      integer :: check
+    
+      !real(wp) :: intensity(index_mass)
+      real(wp) :: xmass
+      real(wp) :: isotope_masses(index_mass)
+      real(wp) :: exact_intensity(index_mass)
+      real(wp) :: chrg
+
+      real(wp) :: list_masses(10000)
+      real(wp) :: intensity(10000)
+
+      real(wp) :: mass_diff
+    
+      !real(wp), allocatable :: list_masses(:)
+      !real(wp), allocatable :: save_list(:)
+      !real(wp), allocatable :: save_int(:)
+      !real(wp), allocatable :: intensity(:)
+      !real (wp) :: save_list(1000)
+      !real (wp) :: save_list(1000)
+
+      logical :: there = .true.
+
+      xmass = 0
+      loop = 0
+      loop2 = 0
+      check = 0
+      !count_mass = count_mass + index_mass
+      if(count_mass == 0)then
+        sum_index =  index_mass
+      else
+        sum_index = count_mass + index_mass
+      endif
+
+
+      !> loop over the list from the isotope subroutine
+outer: do loop2 = 1, index_mass 
+        loop = 0
+
+        !> loop over all entries of new (check) list 
+inner:  do 
+          loop = loop + 1
+          mass_diff = abs(list_masses(loop) - isotope_masses(loop2))
+
+          if ( list_masses(loop) == 0.0_wp ) then
+            there = .false.
+             !write(*,*) 'NULL'
+            exit inner
+
+          !elseif  ( list_masses(loop) == isotope_masses(loop2) ) then
+          elseif  ( mass_diff < 1.0d0-10 .or. mass_diff == 0.0_wp) then
+            there = .true.
+            intensity(loop) = intensity(loop) +  1 * exact_intensity(loop2) &
+              * abs(chrg)
+            if (loop2 < index_mass ) cycle outer 
+            if (loop2 == index_mass ) exit inner
+
+
+          !>> false if not in list, store
+          !elseif ( list_masses(loop) /= isotope_masses(loop2) ) then
+          elseif  ( mass_diff > 1.0d0-10 ) then
+            there = .false.
+            if (loop == sum_index ) exit inner
+          endif
+        enddo inner
+
+
+        if ( .not. there ) then
+          count_mass = count_mass + 1
+          list_masses(count_mass) = isotope_masses(loop2)
+          intensity(count_mass) = intensity(count_mass) + 1 * exact_intensity(loop2) &
+            * abs(chrg)
+        endif
+
+      enddo outer
+
+   
+    end subroutine check_entries
+    
+end module count_entries 
diff --git a/isotopes.f90 b/src/isotopes.f90
similarity index 95%
rename from isotopes.f90
rename to src/isotopes.f90
index 3143839..d20c768 100644
--- a/isotopes.f90
+++ b/src/isotopes.f90
@@ -16,7 +16,7 @@ module isotope_pattern
   contains
 
 subroutine isotope(counter, mzmin, ntot, iat_save, maxatm, rnd, &
-    no_isotopes, index_mass, exact_intensity, isotope_masses)
+    no_isotopes, index_mass, exact_intensity, isotope_masses, z_chrg)
 
   integer :: ntot,iat_save(*),maxatm
   integer :: niso(200)
@@ -27,6 +27,7 @@ subroutine isotope(counter, mzmin, ntot, iat_save, maxatm, rnd, &
 !  integer :: tmp_intensity
   integer :: store_int(1000)
   integer :: mzmin
+  integer :: z_chrg
 
   real(wp) :: rnd(nrnd,maxatm)
   real(wp) :: r,sum_prob
@@ -34,7 +35,6 @@ subroutine isotope(counter, mzmin, ntot, iat_save, maxatm, rnd, &
   real(wp) :: list_masses(nrnd)
   real(wp),allocatable :: isotope_masses(:)
 
-  real(wp) :: save_mass(nrnd)
   real(wp) :: current_mass
 
   real(wp), allocatable :: exact_intensity(:)
@@ -126,6 +126,19 @@ subroutine isotope(counter, mzmin, ntot, iat_save, maxatm, rnd, &
         prob(17,2)        = 24.24_wp
         massiso(17,1)     = 34.968852_wp
         massiso(17,2)     = 36.965902_wp
+
+   ! 20 Ca (Calcium)
+        niso(20)          = 5
+        prob(20,1)        = 96.94_wp
+        prob(20,2)        = 0.65_wp
+        prob(20,3)        = 0.14_wp
+        prob(20,4)        = 2.09_wp
+        prob(20,5)        = 0.18_wp
+        massiso(20,1)     = 39.962591_wp
+        massiso(20,2)     = 41.958618_wp
+        massiso(20,3)     = 42.958766_wp
+        massiso(20,4)     = 43.955482_wp
+        massiso(20,5)     = 45.953688_wp      
   
    ! 22 Ti (Titanium) 
         niso(22)          = 5           
@@ -344,6 +357,13 @@ subroutine isotope(counter, mzmin, ntot, iat_save, maxatm, rnd, &
           prob(53,1)      = 100.00_wp
           massiso(53,1)   = 126.904473_wp
 
+   ! 57 La (Lanthanum)
+          niso(57)        = 2          
+          prob(57,1)      = 0.09_wp
+          prob(57,2)      = 99.91_wp
+          massiso(57,1)   = 137.907112_wp
+          massiso(57,2)   = 138.909477_wp
+
    ! 74 W (Tungsten)
           niso(74)        = 5          
           prob(74,1)      = 0.12_wp
@@ -414,7 +434,6 @@ subroutine isotope(counter, mzmin, ntot, iat_save, maxatm, rnd, &
   ! postprocessing starts here 
   
   prob = prob * 0.01_wp
-  save_mass = 0.0_wp
   list_masses = 0.0_wp
   index_mass = 0
   loop = 0
@@ -463,7 +482,8 @@ subroutine isotope(counter, mzmin, ntot, iat_save, maxatm, rnd, &
       enddo
       xmass = xmass + x
     enddo
-      current_mass = xmass !/ real(abs(z_chrg),wp)
+
+      current_mass = xmass / real(abs(z_chrg),wp)
 
       there = .true.
       if ( current_mass > mzmin ) then 
@@ -519,7 +539,7 @@ subroutine isotope(counter, mzmin, ntot, iat_save, maxatm, rnd, &
          xmass = xmass + x
       enddo
 
-      current_mass = xmass !/ float(abs(z_chrg))
+      current_mass = xmass / float(abs(z_chrg))
 
       there = .true.
       !> only values larger than user input 
diff --git a/main.f90 b/src/main.F90
similarity index 60%
rename from main.f90
rename to src/main.F90
index c74deb9..1291e23 100644
--- a/main.f90
+++ b/src/main.F90
@@ -35,9 +35,12 @@
 program plotms
   use count_entries, only: check_entries
   use isotope_pattern, only: isotope
+  use version, only: print_version 
   use qcxms_boxmuller, only: vary_energies
-  use qcxms_readcommon
+  use readcommon
+  use mctc_env, only : error_type, get_argument
   use xtb_mctc_accuracy, only: wp
+  use xtb_mctc_convert
   use xtb_mctc_symbols, only: toSymbol
   implicit none
 
@@ -58,6 +61,7 @@ program plotms
   integer :: sorted_index
   integer :: list_length
   integer :: exp_entries
+  integer :: iarg, narg
 
   real(wp) :: xx(100),tmax,r,rms,norm,cthr,cthr2
   real(wp) :: chrg,chrg2,checksum,score
@@ -78,21 +82,43 @@ program plotms
   !real(wp), allocatable :: intensity(:)
   real(wp) :: list_masses(10000)
   real(wp) :: intensity(10000)
+  real(wp) :: mmax
 
-  logical  :: sel,verbose,exdat,small
+  logical  :: sel,verbose,small
+  logical  :: expdat, nistdat
   logical  :: ex,ex1,ex2,ex3,ex4
   logical  :: noIso, Plasma
-  logical  :: args = .false.
   
   ! fname=<qcxms.res> or result file, xname contains the mass.agr plot file
-  character(len=80)  :: arg(10)
   character(len=80)  :: xname
   character(len=:), allocatable  :: fname,fname1,fname2,fname3,fname4
   character(len=4096), external :: fullpath
-
-  verbose          = .false.
+  character(len=:), allocatable  :: exp_dat
+  character(len=:), allocatable :: arg
+
+  !!!!!!!!!!!!!!!!!!!!!
+  integer :: sm
+  integer, allocatable :: int_exp(:), int_thr(:)
+  integer :: store_check_list
+  integer :: new_length_thr, new_length_exp
+  real(wp) :: store_intensities
+  real(wp), allocatable :: added_thr_intensities(:), added_exp_intensities(:)
+  real(wp), allocatable :: added_thr_masses(:), added_exp_masses(:)
+  real(wp) :: store_thr_int(1000)
+  real(wp) :: store_exp_int(1000)
+  real(wp) :: store_thr_mass(1000)
+  real(wp) :: store_exp_mass(1000)
+  !real(wp) :: store_check_list
+  !integer, allocatable :: added_masses(:)
+  !integer, allocatable :: exp_mass (:)
+  !integer :: store_mass(1000)
+  !!!!!!!!!!!!!!!!!!!!!
+
+  expdat        = .false.
+  verbose       = .false.
   small         = .false.
   isec          = 0
+  iarg          = 0
   norm          = 1.0
   nagrfile      = 410
   mzmin         = 10
@@ -115,72 +141,105 @@ program plotms
  !xname='~/.mass_raw.agr'
  !xname='~/.mass_jay.agr'
   fname=''
-  
-  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-  ! start loop reading arguments
-  do i=1,9
-     arg(i)=' '
-    call get_command_argument(i,arg(i))
-    if (arg(i) /= ' ') args = .true. 
-  enddo
-  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+  exp_dat="exp.dat"
   
   ! start loop processing aruments
   
   !  comand line parameters
-  !  -a count charges from -1000 (cthr) to cthr2
-  !  -v print spectra "mass % intensity  counts   Int. exptl" to stdout;
-  !     with "Int. exptl" (experimental) taken from exp.dat but not all exp peaks are exported
-  !     if no theoretical counterpart exists
-  !  -f filename or  -f <name_of_res_file>
-  !  -t couting ions with charge x to y (give the value, e.g. "-t 1 2" for charge 1 to 2)
-  !  -w broadening the charges by an SD 
-  !  -s Take only secondary and tertiary fragmentations (give the value, e.g. "-s 2" for secondary)
-  !  -m set minimum value for m/z, so 100% value will be calc. for higher values (x-axis)
-  !  -i set the minimum rel. intensity at which the signals are counted          (y-axis)
-  !  -p DO NOT calculate isotope pattern
-  
-  do i = 1, 9
-     if(index(arg(i),'-a') /= 0)  cthr   = -1000.0_wp
-     if(index(arg(i),'-v') /= 0)  verbose   = .true.
-     if(index(arg(i),'-f') /= 0)  fname  = arg(i+1)
-     if(index(arg(i),'-p') /= 0)  noIso  = .true.
-
-     ! if = 0, unity intensities are regarded
-     if(index(arg(i),'-t') /= 0) then
-        call readl(arg(i+1),xx,nn)
-        cthr=xx(1)
-     endif
-
-     ! set width distr. of boltz sampling
-     if(index(arg(i),'-w') /= 0) then
-        call readl(arg(i+1),xx,nn)
-        chrg_wdth=xx(1)
-     endif
-
-     ! set number of cascading runs
-     if(index(arg(i),'-s') /= 0) then
-        call readl(arg(i+1),xx,nn)
-        isec=int(xx(1))
-     endif
-
-     ! set minimum mass
-     if(index(arg(i),'-m') /= 0)then
-        call readl(arg(i+1),xx,nn)
-        mzmin=int(xx(1))
-     endif
-
-     ! get initial charge of system
-     if(index(arg(i),'-c') /= 0)then
-        call readl(arg(i+1),xx,nn)
-        total_charge = real(xx(1),wp)
-     endif
-
-     ! set the minimum intensity
-     if(index(arg(i),'-i') /= 0)then
-        call readl(arg(i+1),xx,nn)
-        min_intensity = real(xx(1),wp)
-     endif
+  !> -a count charges from -1000 (cthr) to cthr2
+  !> -v print spectra "mass % intensity  counts   Int. exptl" to stdout;
+  !     with "Int. exptl" (experimental) taken from exp.dat but not all 
+  !     exp peaks are exported if no theoretical counterpart exists
+  !> -f filename or  -f <name_of_res_file>
+  !> -t couting ions with charge x to y (give the value, e.g. "-t 1 2" 
+  !     for charge 1 to 2)
+  !> -w broadening the charges by an SD 
+  !> -s Take only secondary and tertiary fragmentations (give the value, 
+  !      e.g. "-s 2" for secondary)
+  !  -m set minimum value for m/z, so 100% value will be calc. for higher values (CID)
+  !  -p calculate NO isotope pattern
+  !  -i set minimum intensity that is considered in rel. intensity percent 
+  !  -e provide exp. input file (in .csv format)
+
+  narg = command_argument_count()
+
+  do while(iarg < narg)
+    iarg = iarg + 1
+    call get_argument(iarg, arg)
+
+    select case(arg)
+     !if(index(arg(i),'-a') /= 0)  cthr   = -1000.0_wp
+     !if(index(arg(i),'-v') /= 0)  verbose   = .true.
+     !if(index(arg(i),'-f') /= 0)  fname  = arg(i+1)
+     !if(index(arg(i),'-p') /= 0)  noIso  = .true.
+     !if(index(arg(i),'-e') /= 0) exp_dat = arg(i+1)
+
+
+   case("-a")                 
+     cthr    = -1000.0_wp
+   case("-v","--verbose")     
+     verbose = .true.
+   case("-p","--noisotope")   
+     noIso   = .true.
+
+   case("-t","--unity")
+     iarg = iarg + 1
+     call get_argument(iarg, arg)
+     call readl(arg,xx,nn)
+     cthr = real(xx(1),wp)
+
+  !> -f filename or  -f <name_of_res_file>
+   case("-f","--file")        
+    iarg = iarg + 1
+    call get_argument(iarg, arg)
+    fname   = arg
+
+  !  -e provide exp. input file (in .csv format)
+   case("-e","--exp")         
+    iarg = iarg + 1
+    call get_argument(iarg, arg)
+    exp_dat = arg
+
+   ! set width distr. of boltz sampling
+   case("-w","--width")
+    iarg = iarg + 1
+    call get_argument(iarg, arg)
+    call readl(arg,xx,nn)
+    chrg_wdth = real(xx(1),wp)
+
+   ! set number of cascading runs
+   case("-s","--cascades")
+    iarg = iarg + 1
+    call get_argument(iarg, arg)
+    call readl(arg,xx,nn)
+    isec = int(xx(1))
+
+   ! set minimum mass
+   case("-m","--min")
+    iarg = iarg + 1
+    call get_argument(iarg, arg)
+    call readl(arg,xx,nn)
+    mzmin=int(xx(1))
+
+   ! set minimum intensity that is considered for the output 
+   ! default: >1%. For all (>0%): set = 0
+   case("-i","--mzmin")
+    iarg = iarg + 1
+    call get_argument(iarg, arg)
+    call readl(arg,xx,nn)
+    min_intensity = real(xx(1),wp)
+
+   ! get initial charge of system <- not used anymore
+   case("-c","--charge")
+    iarg = iarg + 1
+    call get_argument(iarg, arg)
+    call readl(arg,xx,nn)
+    total_charge = real(xx(1),wp)
+
+
+    case default
+      error stop ' -- Unrecognized Keyword -- '
+    end select
   enddo
 
   
@@ -238,29 +297,26 @@ program plotms
   spec = 1 ! EI
   endif
 
+  call print_version
   
-  write(*,*)
-  write(*,'(6x,''* * * * * * * * * * * * * * * * * *'')')
-  write(*,'(6x,''*           P l o t M S           *'')')
-  write(*,'(6x,''* * * * * * * * * * * * * * * * * *'')')
-  write(*,'(6x,''*    QCxMS spectra plotting tool  *'')')
-  write(*,'(6x,''*         -  v. 6.0.1  -          *'')')
-  write(*,'(6x,''*          04. Dec 2021           *'')')
-  write(*,'(6x,''*           *   *   *             *'')')
-  write(*,'(6x,''*           S. Grimme             *'')')
-  write(*,'(6x,''*           J. Koopman            *'')')
-  write(*,'(6x,''* * * * * * * * * * * * * * * * * *'')')
-  write(*,'(6x,''   Contributor:  C.Bauer, T.Kind   '')')
-  write(*,*)
-  write(*,'(6x,''   -> Reading file: '',(a)         )')trim(fname)
+  write(*,'(6x,''-> Reading .res file: '',2x,(a))')trim(fname)
+
+  !> write out if compared
+  if ( exp_dat == 'exp.dat') then
+    inquire(file='exp.dat',exist=expdat)
+  elseif (exp_dat /= 'exp.dat') then
+    inquire(file=exp_dat,exist=expdat)
+  endif
+  if (expdat) write(*,'(6x,''-> Experimental file: '',2x, (a))') exp_dat
+
+  !> give info about xmgrace file (if verbose)
   if (verbose) write(*,'(6x ''   -> xmgrace file body '',(a)         )')trim(xname)
   write(*,*)
-  write(*,*)
   
   ! ------------------------------------------------------------------------------------------------------!
   ! execute arguments
  
-  if (args) then
+  if (narg > 0 ) then
     write(*,'(50(''!''))')
     write(*,'('' The following settings are being used :  '')')
     write(*,*)
@@ -291,11 +347,11 @@ program plotms
     endif
 
     ! -t (choose if unity intensities or normal)
-    if(cthr >= 0)then
-      write(*,'('' - couting ions with charge from '',f4.1,'' to '',f4.1)')   cthr,cthr2 + total_charge
-    else
-      write(*,'('' - counting all fragments with unity charge (frag. overview)'')')
-    endif
+    !if(cthr >= 0)then
+    !  write(*,'('' - couting ions with charge from '',f4.1,'' to '',f4.1)')   cthr,cthr2 + total_charge
+    !else
+    !  write(*,'('' - counting all fragments with unity charge (frag. overview)'')')
+    !endif
     write(*,*)
     write(*,'(50(''!''))')
   endif
@@ -322,12 +378,12 @@ program plotms
     !write(*,*) 'COUNTER', counter
 
     if (spec == 1) then    !EI
-      read(io_spec,*,iostat=io) chrg2, irun, jsec, nf, atm_types, (iat(kk),nat(kk), kk = 1, atm_types)
+      read(io_spec,*,iostat=io) chrg2, z_chrg, irun, jsec, nf, atm_types, (iat(kk),nat(kk), kk = 1, atm_types)
       if(io<0) exit !EOF
       if(io>0) stop ' -- Fail in read -- ' !fail
   
     elseif(spec == 2) then !CID
-      read(io_spec,*,iostat=io) chrg2, irun, jcoll, jsec, nf, atm_types, (iat(kk), nat(kk), kk = 1, atm_types)
+      read(io_spec,*,iostat=io) chrg2, z_chrg, irun, jcoll, jsec, nf, atm_types, (iat(kk), nat(kk), kk = 1, atm_types)
       if(io<0) exit !EOF
       if(io>0) stop ' -- Fail in read -- ' !fail
 
@@ -338,12 +394,27 @@ program plotms
 
 
     if (isec > 0 .and. isec /= jsec) cycle !check tertiary,etc fragmentation (isec)
-  
-    if (chrg2 > cthr) then  !default: chrg2 > 0.001
-      ntot = sum(nat(1:atm_types))
-      if ( ntot > maxatm ) maxatm = ntot  !get highest number of atoms in fragment
+ 
+    if ( z_chrg > 0 ) then
+      if (chrg2 > cthr) then  !default: chrg2 > 0.001
+        ntot = sum(nat(1:atm_types))
+        if ( ntot > maxatm ) maxatm = ntot  !get highest number of atoms in fragment
+        if ( z_chrg > int(total_charge) ) total_charge = real( z_chrg, wp )
+      endif
+    elseif ( z_chrg < 0 ) then
+      if (chrg2 < -1.0_wp*cthr) then  !default: chrg2 > 0.001
+        ntot = sum(nat(1:atm_types))
+        if ( ntot > maxatm ) maxatm = ntot  !get highest number of atoms in fragment
+        if ( z_chrg < int(total_charge) ) total_charge = real( z_chrg, wp )
+      endif
     endif
 
+
+    !if (chrg2 > cthr) then  !default: chrg2 > 0.001
+    !  ntot = sum(nat(1:atm_types))
+    !  if ( ntot > maxatm ) maxatm = ntot  !get highest number of atoms in fragment
+    !endif
+
     i = i + 1 !count number of single fragments with charge > chrt
     if ( irun > maxrun ) maxrun = irun !save highest run number
   
@@ -405,12 +476,12 @@ program plotms
 
     !> read the fragment entry from qcxms.res line by line
     if (spec == 1) then    !EI
-       read(io_spec,*,iostat=io) chrg2,  irun, jsec, nf, atm_types, (iat(kk),nat(kk),kk=1,atm_types)
+       read(io_spec,*,iostat=io) chrg2, z_chrg, irun, jsec, nf, atm_types, (iat(kk),nat(kk),kk=1,atm_types)
        if(io<0) exit !EOF
        if(io>0) stop !fail
   
     elseif(spec == 2) then !CID
-       read(io_spec,*,iostat=io) chrg2, irun, jcoll, jsec, nf, atm_types, (iat(kk),nat(kk),kk=1,atm_types)
+       read(io_spec,*,iostat=io) chrg2, z_chrg, irun, jcoll, jsec, nf, atm_types, (iat(kk),nat(kk),kk=1,atm_types)
        if(io<0) exit !EOF
        if(io>0) stop !fail
 
@@ -427,11 +498,19 @@ program plotms
     if ( cthr < 0 ) chrg = total_charge
 
     !> count the moment where fragments were created (first/second MD or collision...)
+    !if ( (z_chrg > 0 .and. chrg > cthr) .or. (z_chrg < 0 .and. chrg < -1* cthr) ) then   ! default: yes
     if ( abs(chrg) > cthr )  then   ! default: yes
       sel = .true.
       ial = ial + 1              !count total amount of fragmentations
       jal(jsec) = jal(jsec) + 1  !count amount of first, sec., tert., ... fragmentations
 
+      !> if not fragmented (i.e. smaller/larger than total_charge) count it to kal(1)
+      !if ( abs(chrg) < abs(total_charge) ) then
+      !  kal(jcoll) = kal(jcoll) + 1 !count the collisions
+      !else
+      !  kal(1) = kal(jcoll) + 1     !no fragmentation
+      !endif
+
 
       !> count the collision at which most framentation occured
       if ( spec == 2 ) then
@@ -466,7 +545,7 @@ program plotms
       !> compute isotope patterns via monte carlo and save intensites 
       !  of all possible combinations 
       call isotope (counter, mzmin, ntot, iat_save, maxatm, rnd, &
-        noIso, index_mass, exact_intensity, isotope_masses)
+        noIso, index_mass, exact_intensity, isotope_masses, z_chrg)
 
       !>> distribute charge (if set as input)
       if(chrg_wdth > 1.0d-6) chrg = vary_energies(chrg,chrg_wdth) 
@@ -488,10 +567,13 @@ program plotms
 
   list_length=0
 
+  !if (z_chrg == 1) extra_mass = z_chrg * amutoau !init for electron mass
+
   !> find the highest intensity
   tmax = maxval(intensity)
 
-  intensity(:) = intensity(:)/tmax * 1000.0_wp
+  !> normalize to 100%
+  intensity(:) = intensity(:)/tmax * 100.0_wp
 
   allocate(reduced_masses(count_mass), reduced_intensities(count_mass))
 
@@ -567,18 +649,18 @@ program plotms
   imax=0
   imin=0
   
-  inquire(file='exp.dat',exist=exdat)
+  inquire(file='nist.dat',exist=nistdat)
+
   
-  if(exdat) then
-    write(*,*) 'Reading exp.dat ...'
-    open( file = 'exp.dat', newunit = io_exp, status = 'old')
+  if(nistdat) then
+    write(*,*) 'Reading nist.dat ...'
+    open( file = 'nist.dat', newunit = io_exp, status = 'old')
   
-    !> read the experimental (NIST) file 
+    !> read the experimental (NIST/JCAMP) file 
 rd: do
       read(io_exp,'(a)',iostat=iocheck)line
       if (iocheck < 0) exit rd
 
-  
       !> read the maximum intensity of exp.
       if(index(line,'##MAXY=') /= 0)then
         line(7:7)=' '
@@ -615,22 +697,89 @@ program plotms
              kk = kk + 1
              exp_mass(kk) = xx(2 * k - 1)
              exp_int (kk) = xx(2 * k)
-             if(exp_mass(kk) > imax) imax = exp_mass(kk)
-             if(exp_int (kk) < imin) imin = exp_int (kk)
+             !if(exp_mass(kk) > imax) imax = exp_mass(kk)
+             !if(exp_int (kk) < imin) imin = exp_int (kk)
           enddo
         enddo
       endif
     enddo rd
-  
+
+    imax = maxval(exp_mass)
+    !imin = minval(exp_mass)
+
+    mmax = maxval(exp_int)
+
+    ! bring exp to the right order of magnitude 
+    do i = 1, exp_entries
+      exp_int(i) = exp_int(i) / norm
+    enddo
+  endif
+
+  !!!!!!!!!!!!!!!!!!!!!
+  !> if it is a csv file
+
+
+
+  if (expdat) then
+    write(*,*) 'Reading ', exp_dat,' ...'
+    open( file = exp_dat, newunit = io_exp, status = 'old')
+
+    exp_entries = 0
+
+    !>> count the entries
+    do
+      read(io_exp,'(a)',iostat=iocheck)!line
+      if (iocheck < 0) exit 
+
+      exp_entries = exp_entries + 1
+    enddo
+
+    rewind(io_exp)
+
+    !>> allocate memory
+    allocate (exp_mass(exp_entries), &
+      &       exp_int(exp_entries))
+
+    kk = 0
+    iocheck=0
+
+    !>> count the intensities and masses
+    do kk = 1, exp_entries
+      read(io_exp,'(a)',iostat=iocheck)line
+      if (iocheck < 0) exit 
+
+      do k=1,80
+        if(line(k:k) == ',') then
+          line(k:k)=' '
+        endif
+      enddo
+
+      call readl(line,xx,nn)
+
+      exp_mass(kk) = xx(1)
+      exp_int (kk) = xx(2)
+    enddo 
     close(io_exp)
+
+    imax = maxval(exp_mass)
+    !imin = minval(exp_mass)
+
+    mmax = maxval(exp_int)
+
+    do kk = 1, exp_entries
+      exp_int (kk) = (exp_int(kk) / mmax) *100.0_wp
+    enddo
+
+  
   endif
+
   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  
   !> get the minimum m/z value that is to be plotted
   imin = mzmin
 
   !> get the maximum m/z value that is to be plotted
-  imax = nint(maxval(sorted_masses))
+  if (imax < nint(maxval(sorted_masses))) imax = nint(maxval(sorted_masses))
 
   ! counts of structures in the 100% peak
   write(*,*) 'Theoretical counts in 100 % signal:', idint(tmax)
@@ -751,22 +900,24 @@ program plotms
  
     !> Write out the results into the mass.agr file !
     do i = 1, list_length ! count_mass 
-      write(io_mass,*) sorted_masses(i), sorted_intensities(i)/10.0_wp 
+      write(io_mass,*) sorted_masses(i), sorted_intensities(i)
     enddo
 
     write(io_mass,*)'&'
     !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-    ! TK establish again if exdat (experimental JCAMPDX) exists
+    ! TK establish again if expdat (experimental JCAMPDX) exists
     ! TK exp_mass(i) - contains the exp masses and  exp_int(i) contains the abundance
     ! TK  exp_entries contains number of experimental spectra
   
-    if(exdat)then
+    if(nistdat .or. expdat)then
+
       write(io_mass,*)'@target G0.S2'
       write(io_mass,*)'@type bar'
       do i=1,exp_entries
-         write(io_mass,*) exp_mass(i),-exp_int(i)/norm
+         write(io_mass,*) exp_mass(i),-exp_int(i)
       enddo
       write(io_mass,*)'&'
+
     endif
 
   endif !ex
@@ -776,35 +927,169 @@ program plotms
   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
   
  ! compute deviation exp-theor.
-  if(exdat)then
+  if(expdat .or. nistdat)then
 
     rms  = 0
     nn   = 0
     kkk  = 0
     kkkk = 0
 
-ol: do i = 1, exp_entries
-il:   do j = 1, list_length
-        if ( exp_int(i)/norm > 5.0_wp )then !.and. sorted_intensities(j) > 1.0_wp )then
-          if ( exp_mass(i) == nint(sorted_masses(j))) then
-            r = sorted_intensities(j) - (exp_int(i) / norm)
-            !write(*,*) i, exp_mass(i), exp_int(i)
-            !write(*,*) j, sorted_masses(j), sorted_intensities(j) 
-            !write(*,*) r
+
+    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    !> this is for integer masses
+    !> calculate integer list of theor. masses
+    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    store_thr_int = 0
+
+    allocate(int_thr(list_length))
+
+    !> transfer to integer
+    do j = 1, list_length 
+      int_thr(j) = nint(sorted_masses(j))
+    enddo
+
+
+    new_length_thr = 0
+    sm = 0
+
+    do i = 1, list_length 
+      store_intensities = 0.0_wp
+
+      store_check_list = int_thr(i)
+
+      if(sm /= store_check_list) new_length_thr = new_length_thr + 1
+
+      do j = 1, list_length
+        if (store_check_list == int_thr(j))then
+          store_intensities = store_intensities + sorted_intensities(j)
+        endif
+
+      enddo
+
+      sm = store_check_list
+
+      store_thr_int (new_length_thr) = store_intensities
+      store_thr_mass(new_length_thr) = store_check_list
+
+      !write(*,*) store_check_list, new_length_thr, added_intensities(new_length_thr)
+        
+    enddo
+
+    allocate(added_thr_intensities(new_length_thr), &
+             added_thr_masses(new_length_thr))
+
+    do i = 1, new_length_thr
+      added_thr_masses(i)      = store_thr_mass(i)
+      added_thr_intensities(i) = (store_thr_int(i)/maxval(store_thr_int)*100.0_wp)
+    !  write(*,*) added_masses(i), added_intensities(i)
+    enddo
+
+
+
+    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    !> for experimental masses in integer
+    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    store_exp_int = 0
+    allocate(int_exp(exp_entries))
+
+    do j = 1, exp_entries 
+      int_exp(j) = nint(exp_mass(j))
+    enddo
+
+    new_length_exp = 0
+    sm = 0
+
+    do i = 1, exp_entries 
+      store_intensities = 0.0_wp
+
+      store_check_list = int_exp(i)
+
+      if(sm /= store_check_list) new_length_exp = new_length_exp + 1
+
+      do j = 1, exp_entries
+        if (store_check_list == int_exp(j))then
+          store_intensities = store_intensities + exp_int(j)
+        endif
+
+      enddo
+
+      sm = store_check_list
+
+      store_exp_int(new_length_exp) = store_intensities
+      store_exp_mass(new_length_exp) = store_check_list
+
+      !write(*,*) store_check_list, new_length_exp, added_intensities(new_length_exp)
+        
+    enddo
+
+    allocate(added_exp_intensities(new_length_exp), &
+             added_exp_masses(new_length_exp))
+
+    do i = 1, new_length_exp
+      added_exp_masses(i)      =  store_exp_mass(i)
+      added_exp_intensities(i) = (store_exp_int(i)/maxval(store_exp_int)*100.0_wp)
+    !  write(*,*) added_masses(i), added_intensities(i)
+    enddo
+
+
+ol: do i = 1, new_length_exp
+il:   do j = 1, new_length_thr
+        if ( added_exp_intensities(i) > 5.0_wp )then 
+          !if ( nint(exp_mass(i)) == added_masses(j) ) then
+          if ( added_exp_masses(i) == added_thr_masses(j) ) then
+            r = added_thr_intensities(j) - added_exp_intensities(i)
             kkk = kkk + 1
-            if ( sorted_intensities(j) > 2.5_wp) kkkk = kkkk + 1
+            if ( added_thr_intensities(j) > 2.5_wp) kkkk = kkkk + 1
             rms = rms + abs(r)
           endif
         endif
       enddo il
     enddo ol
 
+!  new_length = 0
+!  sm = 0
+!  do i = 1, list_length 
+!
+!    store_check_list = sorted_masses(i)
+!
+!    store_intensities = 0.0_wp
+!
+!    do i = 1, list_length
+!      if (sorted_masses(i) - store_check_list <= 1.0d-2)then
+!        store_intensities = store_intensities + sorted_intensities(j)
+!        store_mass = store_intensities + sorted_intensities(j)
+!!        store_intensities = sorted_masses(i) - sorted_masses(i-1)
+!!        write(*,*) i, sorted_masses(i-1), sorted_masses(i), store_intensities
+!      endif
+!    enddo
+!
+!     if(sm /= store_check_list) new_length = new_length + 1
+!     sm = store_check_list
+!
+!  stop
+!
+!
+!
+!ol: do i = 1, exp_entries
+!il:   do j = 1, list_length
+!        if ( exp_int(i) > 5.0_wp )then 
+!          !if ( nint(exp_mass(i)) == added_masses(j) ) then
+!          if ( exp_mass(i) == sorted_masses(j) ) then
+!            r = added_intensities(j) - exp_int(i)
+!            kkk = kkk + 1
+!            if ( added_intensities(j) > 2.5_wp) kkkk = kkkk + 1
+!            rms = rms + abs(r)
+!          endif
+!        endif
+!      enddo il
+!    enddo ol
+
+    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
     write(*,*)'MAD(exptl./theor.) = ', rms / kkk
     write(*,*)'# exptl. > 5 %     = ', kkk
     write(*,*)'% correctly found  = ', 100 * float(kkkk)/float(kkk)
 
-  endif
   
   close(io_spec)
   close(io_raw)
@@ -813,32 +1098,32 @@ program plotms
   close(io_jcamp)
   
   ! compute mass spectral match score
-  if(exdat)then 
     score = 0.0_wp
-    ! bring exp to the right order of magnitude 
-    do i = 1, exp_entries
-      exp_int(i) = exp_int(i) / norm
-    enddo
 
-    write(*,*) 
-    write(*,*) ' !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! '
-    write(*,*) ' - NIST mass comparison not supported in v6.0 - '
-    write(*,*) '   -    no automatic score comparison       -'
-    stop       ' !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! '
+    !write(*,*) 
+    !write(*,*) ' !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! '
+    !write(*,*) ' - NIST mass comparison not supported in v6.0 - '
+    !write(*,*) '   -    no automatic score comparison       -'
+    !write(*,*) ' !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! '
+    !stop       ' !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! '
 
 
-  !  call match(sorted_masses, sorted_intensities, list_length, &
-  !              exp_entries, exp_mass, exp_int,score,tmax)
+    !call match_accurate(sorted_masses, sorted_intensities, list_length, &
+    !            exp_entries, exp_mass, exp_int,score,tmax)
+    !call match(added_masses, added_intensities, new_length, &
+    !            exp_entries, exp_mass, exp_int,score,tmax)
+    call match(added_thr_masses, added_thr_intensities, new_length_thr, &
+                new_length_exp, added_exp_masses, added_exp_intensities,score,tmax)
     write(*,*)
     write(*,*)"!!!!!!!!!!!!!!!!!!!!!!! "
     write(*,*)"  Matching score:  "
-   ! write(*,'(6F10.3)') score   
+    write(*,'(6F10.3)') score   
     write(*,*)"!!!!!!!!!!!!!!!!!!!!!!! "
     write(*,*)
     write(*,*)"Composite match score, see "
     write(*,*)"Stein, S. E.; Scott, D. R. J. Am. Soc. Mass Spectrom. 1994, 5, 859-866" 
-    write(*,*)"For our implementation, see "
-    write(*,*)"Bauer, C. A.; Grimme,S. J. Phys. Chem. A 2014, 118, 11479-11484"
+    !write(*,*)"For our implementation, see "
+    !write(*,*)"Bauer, C. A.; Grimme,S. J. Phys. Chem. A 2014, 118, 11479-11484"
     
   
   endif 
@@ -848,7 +1133,7 @@ end program plotms
  
 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
-subroutine match(sorted_masses, sorted_intensities, list_length, &
+subroutine match(added_masses, added_intensities, new_length, &
                   exp_entries,  exp_mass, exp_int,score,tmax)
   use xtb_mctc_accuracy, only: wp
   implicit none
@@ -856,7 +1141,9 @@ subroutine match(sorted_masses, sorted_intensities, list_length, &
   integer :: i,j
   integer :: pp !peak pair number pp
   integer :: numcalc ! number of calculated peaks
-  integer :: list_length, exp_entries
+  integer :: new_length, exp_entries
+!  integer :: entry, entry2
+  integer :: cnt
 
   !real(wp) :: tmass(10000)
   !real(wp) :: iexp(2,10000)
@@ -864,118 +1151,144 @@ subroutine match(sorted_masses, sorted_intensities, list_length, &
   real(wp) :: exp_int(exp_entries)
   real(wp) :: score
   real(wp) :: tmax
-  real(wp) :: w(2,10000) !weighted vectors
+  real(wp),allocatable :: w_exp(:) !weighted vectors
+  real(wp),allocatable :: w_thr(:) !weighted vectors
+  !real(wp) :: w(2,10000) !weighted vectors
+  !real(wp), allocatable :: w_exp(:) !weighted vectors
+  !real(wp), allocatable :: w_thr(:) !weighted vectors
   real(wp) :: sum1,sum2,sum3,sum4,dot,fr
-  real(wp) :: norm(2)
-  real(wp) :: p(2,10000) ! peak pair matrix 
-  real(wp) :: sorted_masses(list_length), sorted_intensities(list_length)
+  !real(wp) :: norm(2)
+  real(wp) :: norm
+  !real(wp) :: p(2,10000) ! peak pair matrix 
+  real(wp), allocatable :: p(:,:) ! peak pair matrix 
+  real(wp) :: added_masses(new_length)
+  real(wp) :: added_intensities(new_length)
+  !!!!!!!!!!!!!!!
+  !integer :: exp_mass(exp_entries)
+  !integer :: added_masses(new_length)
+  !!!!!!!!!!!!!!!
+
+
+!  numcalc = new_length
+!  entry = 0
+  
+  !allocate( w_exp(exp_entries), &
+  !          w_thr(new_length))
+  
+  !> weighted spectral vectors, m**3, int**0.6 scaling
+  !w = 0.0_wp
+
+  pp = 0
+  !> get weighting of experimental spectrum
+  allocate(w_exp(exp_entries))
+  norm = 0.0_wp
+  do i = 1, exp_entries
+    w_exp(i) = exp_mass(i)**2 * exp_int(i)**0.6_wp
+    norm = norm + w_exp(i)**2
+  enddo 
 
-  numcalc=0
-  
-  !do i = 1, 10000
-  !  if ( tmass(i) /= 0.0_wp ) numcalc = numcalc + 1
-  !enddo
+  norm = sqrt(norm)
 
-  numcalc = list_length
-  
-  !weighted spectral vectors, m**3, int**0.6 scaling
-  w = 0.0_wp
-    !do i = 1, 10000
-    !  do j = 1, 10000
-    !    if ( j == iexp(1, i) ) then
-    !      w(2,j) = j**2 * ( 1000.0_wp * tmass(j) / tmax )**0.6_wp ! changed this to 1000 <- check it!
-    !      w(1,j) = iexp(1,i)**2 * iexp(2,i)**0.6_wp
-    !    endif
-    !  enddo
-    !enddo
-  !do i = 1, 10000
-ol: do i = 1, exp_entries
-il:  do j = 1, list_length
-       if ( sorted_masses(j) == exp_mass(i) ) then
-        !w(2,j) = j**2 * ( 100.0_wp * tmass(j) / tmax )**0.6_wp ! changed this to 1000 <- check it!
-        w(2,j) = j**2 * ( sorted_intensities(j) )**0.6_wp ! changed this to 1000 <- check it!
-        w(1,j) = exp_mass(i)**2 * exp_int(i)**0.6_wp
-      endif
-    enddo il
-  enddo ol
-  
-  norm = 0.0_wp
-  do i = 1, 10000
-     norm(1) = norm(1) + w(1,i)**2
-     norm(2) = norm(2) + w(2,i)**2
+  do i = 1, exp_entries
+     w_exp(i) = w_exp(i) / norm
   enddo
-  
+
+  !> get weighting of calculated spectrum
+  allocate(w_thr(new_length))
+  norm = 0.0_wp
+  do j = 1, new_length
+    w_thr(j) = (added_masses(j))**2 * ( added_intensities(j) )**0.6_wp 
+    norm = norm + w_thr(j)**2
+  enddo 
+
   norm = sqrt(norm)
-  
-  do i = 1, 10000
-     w(1,i) = w(1,i) / norm(1)
-     w(2,i) = w(2,i) / norm(2)
+
+  do j = 1, new_length
+     w_thr(j) = w_thr(j) / norm
   enddo
+
   
   dot  =  0.0_wp
   sum1 =  0.0_wp
   sum2 =  0.0_wp
   sum3 =  0.0_wp
 
-  do i = 1, 10000
-     sum1 = sum1 + w(1,i) * w(2,i)
-     sum2 = sum2 + (w(1,i))**2
-     sum3 = sum3 + (w(2,i))**2
-  enddo
+
+ do i = 1, exp_entries
+   do j = 1, new_length
+        if ( exp_mass(i) == added_masses(j)) then
+          pp = pp + 1
+          sum1 = sum1 +  w_exp(i) * w_thr(j)
+          sum2 = sum2 + (w_exp(i))**2
+          sum3 = sum3 + (w_thr(j))**2
+        endif
+      enddo 
+    enddo 
+
   
   dot = sum1**2 / (sum2 * sum3)
+  !write(*,*) 'DOT', dot
   
+  deallocate(w_exp, w_thr)
+
+  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
   ! masses and intensity scalement for the second term
   ! m**0
   ! int**1
-  
-  w=0.0_wp
-
-  do i = 1, 10000
-     !do j = 1, 10000
-     do j = 1, list_length
-        if ( j == exp_mass(i) ) then
-           w(2,j) = sorted_intensities(j) 
-           w(1,j) = exp_int(i)
-        endif
-     enddo
+  allocate(w_exp(exp_entries), w_thr(new_length))
+
+  norm=0.0_wp
+
+  do i=1, exp_entries
+     !norm = norm + w_exp(i)**2 ! + exp_int(i) !w(1,i)**2
+     norm = norm + exp_int(i)**2 !w(1,i)**2
   enddo
-  
-  !calculate the norm
-  
+
+  norm = sqrt(norm)
+
+  do i=1, exp_entries
+     w_exp(i) = exp_int(i) / norm
+  enddo
+
+  !!!!!!!!!!!!!!!!!!!!
   norm=0.0_wp
-  do i=1, 10000
-     norm(1) = norm(1) + w(1,i)**2
-     norm(2) = norm(2) + w(2,i)**2
+  do j=1, new_length
+     norm = norm + added_intensities(j)**2 !w(2,i)**2
   enddo
-  
+
   norm = sqrt(norm)
   
-  do i = 1, 10000
-     w(1,i) = w(1,i) / norm(1)
-     w(2,i) = w(2,i) / norm(2)
+  do j=1, new_length
+     w_thr(j) = added_intensities(j) / norm
   enddo
   
-  pp   = 0
+  !pp   = 0
+  !p    = 0.0_wp
   sum4 = 0.0_wp
   fr   = 0.0_wp
-  p    = 0.0_wp
-
-  do i = 1, 10000
-     if ( (w(1,i) * w(2,i) ) /= 0) then
-        pp = pp + 1
-        p(1,pp) = w(1,i)
-        p(2,pp) = w(2,i)
-  !         print*,p(1,i),p(2,i)
-     endif
-  enddo
+  cnt = 0
+
+  allocate (p(2,pp))
+
+  do i = 1, exp_entries
+    do j = 1, new_length
+      if ( exp_mass(i) == added_masses(j)) then
+        cnt = cnt + 1
+        p(1,cnt) = w_exp(i)
+        p(2,cnt) = w_thr(j)
+      endif
+    enddo 
+  enddo 
   
   ! ardous loop 
   call calcfr(pp,p,sum4)
-  if (pp == numcalc) sum4 = sum4 + 1.0_wp
+  if (pp == new_length) sum4 = sum4 + 1.0_wp
+  !write(*,*) 'SUM4', sum4
+  !write(*,*) 'numcalc', numcalc
+  !write(*,*) 'numcalc', new_length
   
   fr = sum4 / float(pp)
-  score = (numcalc * dot + pp * fr) / (numcalc + pp)
+  score = (new_length * dot + pp * fr) / (new_length + pp)
   return
 end subroutine match
 
@@ -995,7 +1308,7 @@ subroutine calcfr(pp,pair,sum4)
   
   sum4 = 0.0_wp
   
-  do i = 1, pp
+  do i = 2, pp
      if     (abs((pair(1,i) * pair(2,i-1)) / (pair(1,i-1) * pair(2,i)))   < 1.0_wp)then
   
         sum4 = sum4 + (pair(1,i) * pair(2,i-1)) / (pair(1,i-1) * pair(2,i))
diff --git a/src/meson.build b/src/meson.build
new file mode 100644
index 0000000..b3bddf8
--- /dev/null
+++ b/src/meson.build
@@ -0,0 +1,21 @@
+# This file is part of PlotMS.  
+
+
+srcs += files(
+       'isotopes.f90',
+       'boxmuller.f90',
+       'entries.f90',
+       'version.f90',
+       'readcommon.f90',
+       'readl.f90',
+       'xtb_mctc_accuracy.f90',
+       'xtb_mctc_constants.f90',
+       'xtb_mctc_convert.f90',
+       'xtb_mctc_symbols.f90',
+       'xtb_mctc_resize.f90'
+       )
+
+prog += files(
+  'main.F90',
+)
+
diff --git a/readcommon.f90 b/src/readcommon.f90
similarity index 55%
rename from readcommon.f90
rename to src/readcommon.f90
index 179c9a6..fcef392 100644
--- a/readcommon.f90
+++ b/src/readcommon.f90
@@ -1,8 +1,10 @@
-module qcxms_readcommon
+!module qcxms_readcommon
+module readcommon
   use xtb_mctc_accuracy, only: wp
   implicit none
 
   integer           :: iocheck = 0
   character(len=80) :: line 
 
-end module qcxms_readcommon
+!end module qcxms_readcommon
+end module readcommon
diff --git a/readl.f90 b/src/readl.f90
similarity index 100%
rename from readl.f90
rename to src/readl.f90
diff --git a/src/version.f90 b/src/version.f90
new file mode 100644
index 0000000..5993a91
--- /dev/null
+++ b/src/version.f90
@@ -0,0 +1,23 @@
+module version
+  implicit none
+
+  contains
+
+subroutine print_version
+
+  write(*,*)
+  write(*,'(6x,''* * * * * * * * * * * * * * * * * *'')')
+  write(*,'(6x,''*           P l o t M S           *'')')
+  write(*,'(6x,''* * * * * * * * * * * * * * * * * *'')')
+  write(*,'(6x,''*    QCxMS spectra plotting tool  *'')')
+  write(*,'(6x,''*         -  v. 6.1.0  -          *'')')
+  write(*,'(6x,''*          25. Jul 2022           *'')')
+  write(*,'(6x,''*           *   *   *             *'')')
+  write(*,'(6x,''*           S. Grimme             *'')')
+  write(*,'(6x,''*           J. Koopman            *'')')
+  write(*,'(6x,''* * * * * * * * * * * * * * * * * *'')')
+  write(*,'(6x,''   Contributor:  C.Bauer, T.Kind   '')')
+  write(*,*)
+
+end subroutine print_version
+end module version
diff --git a/xtb_mctc_accuracy.f90 b/src/xtb_mctc_accuracy.f90
similarity index 100%
rename from xtb_mctc_accuracy.f90
rename to src/xtb_mctc_accuracy.f90
diff --git a/src/xtb_mctc_constants.f90 b/src/xtb_mctc_constants.f90
new file mode 100644
index 0000000..4976e72
--- /dev/null
+++ b/src/xtb_mctc_constants.f90
@@ -0,0 +1,38 @@
+! This file is part of xtb.
+!
+! Copyright (C) 2017-2020 Stefan Grimme
+!
+! xtb is free software: you can redistribute it and/or modify it under
+! the terms of the GNU Lesser General Public License as published by
+! the Free Software Foundation, either version 3 of the License, or
+! (at your option) any later version.
+!
+! xtb is distributed in the hope that it will be useful,
+! but WITHOUT ANY WARRANTY; without even the implied warranty of
+! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+! GNU Lesser General Public License for more details.
+!
+! You should have received a copy of the GNU Lesser General Public License
+! along with xtb.  If not, see <https://www.gnu.org/licenses/>.
+
+module xtb_mctc_constants
+   use xtb_mctc_accuracy, only : wp
+   implicit none
+   private
+   real(wp),public,parameter :: pi = 3.1415926535897932384626433832795029_wp
+   real(wp),public,parameter :: pi4 = 3.1415926535897932384626433832795029_wp*4._wp
+!  √π
+   real(wp),public,parameter ::  sqrtpi  = sqrt(pi)
+!  2×π
+   real(wp),public,parameter :: twopi = 2.0_wp * pi
+!  4×π
+   real(wp),public,parameter :: fourpi = 4.0_wp * pi
+!  π/2
+   real(wp),public,parameter :: pihalf = 0.5_wp * pi
+!  2π/3
+   real(wp),public,parameter :: twothirdpi = 2.0_wp * pi / 3.0_wp
+!  Boltzmann constant in Eh/K
+   real(wp),public,parameter :: kB = 3.166808578545117e-06_wp
+!  speed of light c in vacuum in a.u.
+   real(wp),public,parameter :: lightspeed = 137.0359990740_wp
+end module xtb_mctc_constants
diff --git a/src/xtb_mctc_convert.f90 b/src/xtb_mctc_convert.f90
new file mode 100644
index 0000000..266a713
--- /dev/null
+++ b/src/xtb_mctc_convert.f90
@@ -0,0 +1,64 @@
+! This file is part of xtb.
+!
+! Copyright (C) 2017-2020 Stefan Grimme
+!
+! xtb is free software: you can redistribute it and/or modify it under
+! the terms of the GNU Lesser General Public License as published by
+! the Free Software Foundation, either version 3 of the License, or
+! (at your option) any later version.
+!
+! xtb is distributed in the hope that it will be useful,
+! but WITHOUT ANY WARRANTY; without even the implied warranty of
+! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+! GNU Lesser General Public License for more details.
+!
+! You should have received a copy of the GNU Lesser General Public License
+! along with xtb.  If not, see <https://www.gnu.org/licenses/>.
+
+module xtb_mctc_convert
+   use xtb_mctc_accuracy, only : wp
+   use xtb_mctc_constants
+   implicit none
+   private
+!  convert bohr (a.u.) to Ångström and back
+   real(wp),public,parameter :: autoaa = 0.52917726_wp
+   real(wp),public,parameter :: aatoau = 1.0_wp/autoaa
+!  convert Hartree to eV and back
+   real(wp),public,parameter :: autoev = 27.21138505_wp
+   real(wp),public,parameter :: evtoau = 1.0_wp/autoev
+!  convert Hartree to kcal/mol and back
+   real(wp),public,parameter :: autokcal = 627.50947428_wp
+   real(wp),public,parameter :: kcaltoau = 1.0_wp/autokcal
+!  convert Hartree to kJ/mol and back
+   real(wp),public,parameter :: autokj = 2625.49964038_wp
+   real(wp),public,parameter :: kjtoau = 1.0_wp/autokj
+!  convert Hartree to reciproce centimeters/wavenumbers and back
+   real(wp),public,parameter :: autorcm = 219474.63067_wp
+   real(wp),public,parameter :: autowav = autorcm
+   real(wp),public,parameter :: rcmtoau = 1.0_wp/autorcm
+   real(wp),public,parameter :: wavtoau = 1.0_wp/autowav
+!  convert Hartree to nanometers and back
+   real(wp),public,parameter :: autonm = 45.56335266_wp
+   real(wp),public,parameter :: nmtoau = 1.0_wp/autonm
+!  masses
+!  amu -> kg :: conversion from atomic mass units to kg
+!  me  -> kg :: electron mass (a.u.) in kg
+!  amu -> au :: conversion from a.u. to amu
+   real(wp),public,parameter :: amutokg = 1.660539040e-27_wp
+   real(wp),public,parameter :: kgtoamu = 1.0_wp/amutokg
+   real(wp),public,parameter :: metokg  = 9.10938356e-31_wp
+   real(wp),public,parameter :: kgtome  = 1.0_wp/metokg
+   real(wp),public,parameter :: amutoau = amutokg*kgtome
+   real(wp),public,parameter :: autoamu = kgtoamu*metokg
+!  femtosectons to atomic time units
+   real(wp),public,parameter :: fstoau = 41.3413733365614_wp
+   real(wp),public,parameter :: autofs = 1.0_wp/fstoau
+!  Coulomb to atomic charge units (electrons)
+   real(wp),public,parameter :: autoc = 1.6021766208e-19_wp
+   real(wp),public,parameter :: ctoau = 1.0_wp/autoc
+!  Debye to atomic units
+   real(wp),public,parameter :: autod = autoc * lightspeed * autoaa**2 * fstoau * 1.0e+16_wp
+   real(wp),public,parameter :: dtoau = 1.0_wp/autod
+!  convert meter/seconds to au units
+   real(wp),public,parameter :: mstoau = 1.0d0/2.18769126364D+06
+end module xtb_mctc_convert
diff --git a/xtb_mctc_resize.f90 b/src/xtb_mctc_resize.f90
similarity index 100%
rename from xtb_mctc_resize.f90
rename to src/xtb_mctc_resize.f90
diff --git a/xtb_mctc_symbols.f90 b/src/xtb_mctc_symbols.f90
similarity index 100%
rename from xtb_mctc_symbols.f90
rename to src/xtb_mctc_symbols.f90
diff --git a/subprojects/.gitignore b/subprojects/.gitignore
new file mode 100644
index 0000000..63ea916
--- /dev/null
+++ b/subprojects/.gitignore
@@ -0,0 +1 @@
+/*/
diff --git a/subprojects/mctc-lib.wrap b/subprojects/mctc-lib.wrap
new file mode 100644
index 0000000..6b71458
--- /dev/null
+++ b/subprojects/mctc-lib.wrap
@@ -0,0 +1,4 @@
+[wrap-git]
+directory = mctc-lib
+url = https://github.com/grimme-lab/mctc-lib
+revision = v0.2.3