fci

CIPSI algorithm in the full configuration interaction space.

The user point of view

fci performs CIPSI calculations using a stochastic scheme for both the selection and the PT2 contribution,
pt2 computes the PT2 contribution using the wave function stored in the EZFIO database.

The main keywords/options for this module are:

determinants n_det_max : maximum number of Slater determinants in the CIPSI wave function. The fci program will stop when the size of the CIPSI wave function will exceed determinants n_det_max.
perturbation pt2_max : absolute value of the PT2 to stop the CIPSI calculation. Once the abs(PT2) \(<\) perturbation pt2_max, the CIPSI calculation stops.
determinants n_states : number of states to consider in the CIPSI calculation.
determinants read_wf : if false, starts with a ROHF-like determinant, if true, starts with the current wave function(s) stored in the EZFIO directory.

Note

For a multi-state calculation, it is recommended to start with cis or cisd wave functions as a guess.

determinants expected_s2 : expected value of \(\widehat{S^2}\) for the desired spin multiplicity.
determinants s2_eig : if true, systematically add all the determinants needed to have a pure value of \(\widehat{S^2}\). Also, if true, it tracks only the states having the good determinants expected_s2.

This module was created with the cipsi module.

fci

pt2

do_ddci

File : fci/class.irp.f

logical :: do_only_1h1p
logical :: do_only_cas
logical :: do_ddci

In the FCI case, all those are always false

do_only_1h1p

File : fci/class.irp.f

logical :: do_only_1h1p
logical :: do_only_cas
logical :: do_ddci

In the FCI case, all those are always false

do_only_cas

File : fci/class.irp.f

logical :: do_only_1h1p
logical :: do_only_cas
logical :: do_ddci

In the FCI case, all those are always false

save_energy:

File : fci/save_energy.irp.f

subroutine save_energy(E,pt2)

Saves the energy in EZFIO.

Needs:

Called by:

Calls: