Extracting CI coefficients

[vvp-nsk]

Hi!

I wonder how to get CI coefficients using the SHSISCF solver. Specifically, it returns just an integer instead of a float array :

from pyscf import gto, scf, fci
from pyscf.shciscf import shci

b =  1.243
mol = gto.Mole()
mol.build(
verbose = 5,
output = None,
atom = [
    ['C',(  0.000000,  0.000000, -b/2)],
    ['C',(  0.000000,  0.000000,  b/2)], ],
basis = {'C': 'ccpvdz', },
symmetry = True,
symmetry_subgroup = 'D2h',
spin = 0
)

# Create HF molecule
mf = scf.RHF( mol )
mf.conv_tol = 1e-9
mf.scf()

# Number of orbital and electrons
norb = 26
nelec = 8

# Create SHCI molecule for just variational opt.
# Active spaces chosen to reflect valence active space.
mch = shci.SHCISCF( mf, norb, nelec )
mch.fcisolver.stochastic = True
mch.fcisolver.nPTiter = 0
mch.fcisolver.sweep_iter = [ 0, 3 ]
mch.fcisolver.DoRDM = True
mch.fcisolver.sweep_epsilon = [ 5e-3, 1e-3 ]
e_tot, e_cas, fcivec, mo, mo_energy =  mch.kernel()
print(type(fcivec),fcivec)

It turns out that the 'fcivec' object is a scalar integer - <class 'int'> 0. However, if the mcscf.CASCI class is used then it returns float array - <class 'pyscf.fci.direct_spin1.FCIvector'> [[ ... ]]

The CI coefficients are needed to proceed further with fci.addons.large_ci addon.

Thank you in advance!

With best regards,
Victor Vysotskiy

[hungpham2017]

Maybe you already figured out but I leave it here in case someone may find this usefull:

• This keyword needs to be included in input.dat: writebestdeterminants numer_of_best_determinants to generate dets.bin. My last PR has also included this so that it can be included directly from the interface:
  mch.fcisolver.writebestdeterminants = 1000000
• The following function read_dice_wavefunction can be used to obtain ci coefficients from dets.bin:
  ci, occa, occb = read_dice_wavefunction('dets.bin')