Fix log density spline extrapolation (#133)

* Add extrapolation limits to DensitySpline

* Handle log/exp cutoffs better

* Comment and clean up extrapolation code

* Set extrapolation cutoff limit to r = r_N

.gitignore

@@ -147,7 +147,7 @@ cython_debug/
 .vscode/
 
 # Raw data files
-atomdb/datasets/*/raw/
+atomdb/datasets/*/db/
 
 # Generated documentation
 docs/source/api/

atomdb/species.py

@@ -15,35 +15,23 @@
 
 r"""AtomDB, a database of atomic and ionic properties."""
 
-from dataclasses import dataclass, field, asdict
-
-from glob import glob
-
-from importlib import import_module
-
 import json
-
+import re
+from dataclasses import asdict, dataclass, field
+from importlib import import_module
 from numbers import Integral
-
 from os import makedirs, path
 
-from msgpack import packb, unpackb
-
-from msgpack_numpy import encode, decode
-
 import numpy as np
-
-from numpy import ndarray
-
 import pooch
-import re
 import requests
-
+from msgpack import packb, unpackb
+from msgpack_numpy import decode, encode
+from numpy import ndarray
 from scipy.interpolate import CubicSpline
 
-from atomdb.utils import DEFAULT_DATASET, DEFAULT_DATAPATH, DEFAULT_REMOTE
-from atomdb.periodic import element_symbol, Element
-
+from atomdb.periodic import Element, element_symbol
+from atomdb.utils import DEFAULT_DATAPATH, DEFAULT_DATASET, DEFAULT_REMOTE
 
 __all__ = [
     "Species",
@@ -166,7 +154,9 @@ def __init__(self, x, y, log=False):
         self._log = log
         self._obj = CubicSpline(
             x,
-            np.log(y) if log else y,
+            # Clip y values to >= ε^2 if using log because they have to be above 0;
+            # having them be at least ε^2 seems to work based on my testing
+            np.log(y.clip(min=np.finfo(float).eps ** 2)) if log else y,
             axis=0,
             bc_type="not-a-knot",
             extrapolate=True,
@@ -192,7 +182,9 @@ def __call__(self, x, deriv=0):
         if not (0 <= deriv <= 2):
             raise ValueError(f"Invalid derivative order {deriv}; must be 0 <= `deriv` <= 2")
         elif self._log:
-            y = np.exp(self._obj(x))
+            # Get y = exp(log y). We'll handle errors from small log y values later.
+            with np.errstate(over="ignore"):
+                y = np.exp(self._obj(x))
             if deriv == 1:
                 # d(ρ(r)) = d(log(ρ(r))) * ρ(r)
                 dlogy = self._obj(x, nu=1)
@@ -201,9 +193,13 @@ def __call__(self, x, deriv=0):
                 # d^2(ρ(r)) = d^2(log(ρ(r))) * ρ(r) + [d(ρ(r))]^2/ρ(r)
                 dlogy = self._obj(x, nu=1)
                 d2logy = self._obj(x, nu=2)
-                y = d2logy.flatten() * y + dlogy.flatten() ** 2 * y
+                y = d2logy.flatten() * y + dlogy.flatten() ** 2 / y
         else:
             y = self._obj(x, nu=deriv)
+        # Handle errors from the y = exp(log y) operation -- set NaN to zero
+        np.nan_to_num(y, nan=0., copy=False)
+        # Cutoff value: assume y(x) is zero where x > final given point x_n
+        y[x > self._obj.x[-1]] = 0
         return y
 
 
@@ -218,7 +214,7 @@ def default(self, obj):
             return JSONEncoder.default(self, obj)
 
 
-class _AtomicOrbitals(object):
+class _AtomicOrbitals:
     """Atomic orbitals class."""
 
     def __init__(self, data) -> None:
@@ -883,13 +879,13 @@ def datafile(
                 url=f"{remotepath}{dataset.lower()}/db/repodata.txt",
                 known_hash=None,
                 path=path.join(datapath, dataset.lower(), "db"),
-                fname=f"repo_data.txt",
+                fname="repo_data.txt",
             )
         # if the file is not found or remote was not valid, use the local repodata file
         except (requests.exceptions.HTTPError, ValueError):
             repodata = path.join(datapath, dataset.lower(), "db", "repo_data.txt")
 
-        with open(repodata, "r") as f:
+        with open(repodata) as f:
             data = f.read()
             files = re.findall(rf"\b{elem}+_{charge}+_{mult}+_{nexc}\.msg\b", data)
             species_list = []