add example to set MC-DCFT functional parameters

examples/mcdcft/04_functional_parameter.py

@@ -0,0 +1,35 @@
+from pyscf import scf, gto, mcdcft
+
+'''
+This input file performs a single point energy calculation of H2 with DC24.
+It demonstrates how users can define custom density coherence functionals,
+especially how functional parameters can be set.
+'''
+
+mol = gto.M(atom='H 0 0 0; H 0 0 0.74', basis='def2-tzvp',
+      symmetry=False, verbose=3, unit='angstrom')
+mf = scf.RHF(mol)
+mf.kernel()
+
+# Define a preset for the DC24 functional, which contains functional parameters.
+preset = {
+    # Display name of the new functional. It will be used in displayed messages and chkfiles.
+    'display_name': 'DC24_custom',
+    # Ratio of the MCSCF exchange-correlation energy
+    'hyb_x': 4.525671e-01,
+    # Functional parameters. We will set the functional parameters of HCTH407 (LibXC
+    #     functional 164) with the values listed here. The meaning of each parameter
+    #     can be obtained from the `xc-info` utility provided by LibXC.
+    'params': {164: [8.198942e-01, 4.106753e+00, -3.716774e+01, 1.100812e+02, -9.600026e+01,
+                     1.352989e+01, -6.881959e+01, 2.371350e+02, -3.433615e+02, 1.720927e+02,
+                     1.134169e+00, 1.148509e+01, -2.210990e+01, -1.006682e+02, 1.477906e+02]},
+}
+
+# DC24 is based on HCTH407 functional form. We put "HCTH407" as xc_code.
+mc = mcdcft.CASSCF(mf, 'HCTH407', 2, 2, xc_preset=preset, grids_level=(99, 590))
+e1 = mc.kernel()[0]
+
+# Compare with the results from pre-defined DC24
+e2 = mc.recalculate_with_xc('DC24')[0]
+print("Energy difference:", e1 - e2)
+