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 exceeddeterminants n_det_max.perturbation pt2_max: absolute value of the PT2 to stop the CIPSI calculation. Once the 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 folder.
Note
For a multi-state calculation, it is recommended to start with cis() or cisd()
wave functions as a guess.
determinants s2_eig: if True, systematically add all the determinants needed to have a pure value of \(S^2\). Also, if True, it tracks only the states having the gooddeterminants expected_s2.
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 \(S^2\) for the desired spin multiplicity.
The programmer point of view¶
This module have been created with the cipsi module.
See also
The documentation of the cipsi module.