examples: add lightweight H4 GASSCF example and relocate AlFe2O4+ comparison

Author: yideng2025

examples/mcscf/93_gasscf_h4.py

@@ -0,0 +1,39 @@
+#!/usr/bin/env python
+#
+# Author: Yi Deng <yideng@uchicago.edu>
+#
+
+"""GASSCF orbital optimization for an H4 chain with a restricted GAS space."""
+
+from pyscf import gto, scf
+from pyscf.mcscf import gasscf
+
+
+mol = gto.M(
+    atom="; ".join("H 0 0 %.1f" % z for z in (0.0, 0.8, 1.8, 2.6)),
+    basis="sto-3g",
+    spin=0,
+    verbose=0,
+)
+mf = scf.RHF(mol).run()
+
+# The two active orbitals are split into two one-orbital GAS spaces.  The
+# cumulative bounds enforce one electron after GAS1 and two electrons after
+# GAS2, equivalent to one electron in each GAS space.
+mc = gasscf.GASSCF(
+    mf,
+    ncas=2,
+    nelecas=(1, 1),
+    ncore=1,
+    gas_orbs=(1, 1),
+    gas_restr=((1, 1), (2, 2)),
+    gas_restr_type="cumulative-occ",
+)
+mc.verbose = 4
+e_tot, e_gas, ci, mo, mo_energy = mc.kernel()
+
+print("GASSCF total energy        = %.12f" % e_tot)
+print("GASSCF active-space energy = %.12f" % e_gas)
+print("GASSCF converged           = %s" % mc.converged)
+print("GAS determinant count     = %d" % ci.size)
+

…mcscf/93_gasscf_alfe2o4_plus_fix_spin.py …f_openmolcas/04_alfe2o4_plus_fix_spin.pyexamples/mcscf/93_gasscf_alfe2o4_plus_fix_spin.py renamed to examples/mcscf/gasscf_openmolcas/04_alfe2o4_plus_fix_spin.py examples/mcscf/93_gasscf_alfe2o4_plus_fix_spin.py renamed to examples/mcscf/gasscf_openmolcas/04_alfe2o4_plus_fix_spin.py

@@ -56,7 +56,7 @@
 target_s2 = 20.0  # S=4, multiplicity 9.
 
 here = Path(__file__).resolve().parent
-data_file = here / "gasscf_openmolcas/data/alfe2o4_plus_mo.npz"
+data_file = here / "data/alfe2o4_plus_mo.npz"
 
 with numpy.load(data_file, allow_pickle=False) as data:
     mol = gto.loads(data["mol"].item())