Fix chkfile initial guess problem for ROHF and ROKS (issue pyscf#1986)

pyscf/dft/test/test_he.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import unittest
+import tempfile
 import numpy
 from pyscf import gto
 from pyscf import lib
@@ -191,6 +192,21 @@ def test_convert(self):
         self.assertTrue(isinstance(udks.to_dhf(), scf.dhf.DHF))
         self.assertTrue(isinstance(udks.to_dks('pbe'), dft.dks.DKS))
 
+    # issue 1986
+    def test_init_guess_chkfile(self):
+        with tempfile.NamedTemporaryFile() as tmpf:
+            mol = gto.M(atom='He 0 0 0', basis='631g', charge=1, spin=1)
+            mf = dft.RKS(mol)
+            mf.chkfile = tmpf.name
+            e1 = mf.kernel()
+            mf = dft.RKS(mol)
+            mf.init_guess = 'chkfile'
+            mf.chkfile = tmpf.name
+            mf.max_cycle = 1
+            e2 = mf.kernel()
+            self.assertAlmostEqual(e1, e2, 9)
+
+
 if __name__ == "__main__":
     print("Full Tests for He")
     unittest.main()

pyscf/scf/hf.py

@@ -656,12 +656,28 @@ def init_guess_by_chkfile(mol, chkfile_name, project=None):
     '''Read the HF results from checkpoint file, then project it to the
     basis defined by ``mol``
 
+    Kwargs:
+        project : None or bool
+            Whether to project chkfile's orbitals to the new basis.  Note when
+            the geometry of the chkfile and the given molecule are very
+            different, this projection can produce very poor initial guess.
+            In PES scanning, it is recommended to switch off project.
+
+            If project is set to None, the projection is only applied when the
+            basis sets of the chkfile's molecule are different to the basis
+            sets of the given molecule (regardless whether the geometry of
+            the two molecules are different).  Note the basis sets are
+            considered to be different if the two molecules are derived from
+            the same molecule with different ordering of atoms.
+
     Returns:
         Density matrix, 2D ndarray
     '''
     from pyscf.scf import uhf
     dm = uhf.init_guess_by_chkfile(mol, chkfile_name, project)
-    return dm[0] + dm[1]
+    mo_coeff = dm.mo_coeff[0]
+    mo_occ = dm.mo_occ[0] + dm.mo_occ[1]
+    return lib.tag_array(dm[0] + dm[1], mo_coeff=mo_coeff, mo_occ=mo_occ)
 
 
 def get_init_guess(mol, key='minao'):
@@ -1358,11 +1374,9 @@ def __call__(self, mol_or_geom, **kwargs):
             dm0 = kwargs.pop('dm0')
         elif self.mo_coeff is None:
             dm0 = None
-        elif self.chkfile and h5py.is_hdf5(self.chkfile):
-            dm0 = self.from_chk(self.chkfile)
         else:
             dm0 = None
-            # dm0 form last calculation cannot be used in the current
+            # dm0 form last calculation may not be used in the current
             # calculation if a completely different system is given.
             # Obviously, the systems are very different if the number of
             # basis functions are different.
@@ -1371,6 +1385,8 @@ def __call__(self, mol_or_geom, **kwargs):
             # last calculation.
             if numpy.array_equal(self._last_mol_fp, mol.ao_loc):
                 dm0 = self.make_rdm1()
+            elif self.chkfile and h5py.is_hdf5(self.chkfile):
+                dm0 = self.from_chk(self.chkfile)
         self.mo_coeff = None  # To avoid last mo_coeff being used by SOSCF
         e_tot = self.kernel(dm0=dm0, **kwargs)
         self._last_mol_fp = mol.ao_loc

pyscf/scf/rohf.py

@@ -49,7 +49,28 @@ def init_guess_by_atom(mol):
 
 init_guess_by_huckel = uhf.init_guess_by_huckel
 init_guess_by_mod_huckel = uhf.init_guess_by_mod_huckel
-init_guess_by_chkfile = uhf.init_guess_by_chkfile
+
+def init_guess_by_chkfile(mol, chkfile_name, project=None):
+    '''Read SCF chkfile and make the density matrix for ROHF initial guess.
+
+    Kwargs:
+        project : None or bool
+            Whether to project chkfile's orbitals to the new basis.  Note when
+            the geometry of the chkfile and the given molecule are very
+            different, this projection can produce very poor initial guess.
+            In PES scanning, it is recommended to switch off project.
+
+            If project is set to None, the projection is only applied when the
+            basis sets of the chkfile's molecule are different to the basis
+            sets of the given molecule (regardless whether the geometry of
+            the two molecules are different).  Note the basis sets are
+            considered to be different if the two molecules are derived from
+            the same molecule with different ordering of atoms.
+    '''
+    dm = uhf.init_guess_by_chkfile(mol, chkfile_name, project)
+    mo_coeff = dm.mo_coeff[0]
+    mo_occ = dm.mo_occ[0] + dm.mo_occ[1]
+    return lib.tag_array(dm, mo_coeff=mo_coeff, mo_occ=mo_occ)
 
 def get_fock(mf, h1e=None, s1e=None, vhf=None, dm=None, cycle=-1, diis=None,
              diis_start_cycle=None, level_shift_factor=None, damp_factor=None):