cisd

This module contains a CI of single and double excitations.

The user point of view

The cisd program performs the CI of the ROHF-like + all single and double excitations on top of it. This program can be very useful to :

• Ground state calculations: generate a guess for the ground state wave function if one is not sure that the scf() program gave the lowest SCF solution. In combination with save_natorb() it can produce new MOs in order to reperform an scf() optimization.
• Excited states calculations: generate guess for all the determinants n_states wave functions, that will be used by the fci() program.

The main keywords/options to be used are:

• determinants n_states : number of states to consider for the CISD calculation
• determinants s2_eig : force all states to have the desired value of \(S^2\)
• determinants expected_s2 : desired value of \(S^2\)

The programmer point of view

This module have been built by setting the following rules:

• The only generator determinant is the Hartree-Fock (single-reference method)
• All generated determinants are included in the wave function (no perturbative selection)

These rules are set in the H_apply.irp.f file.

EZFIO parameters

energy

Variational CISD energy

Programs

• cisd

Subroutines / functions

h_apply_cisd:()

File : h_apply.irp.f_shell_8

subroutine H_apply_cisd()

Calls H_apply on the HF determinant and selects all connected single and double excitations (of the same symmetry). Auto-generated by the generate_h_apply script.

Needs:

psi_coef n_states generators_bitmask mo_num mo_two_e_integrals_in_map

h_apply_buffer_allocated n_det s2_eig n_det_generators i_bitmask_gen

n_int psi_det psi_det_generators psi_det_generators

Calls:

build_fock_tmp() copy_h_apply_buffer_to_wf() dsort()

h_apply_cisd_diexc() h_apply_cisd_monoexc()

make_s2_eigenfunction() wall_time()

Touches:

n_det psi_occ_pattern c0_weight

psi_coef psi_det_sorted_bit psi_det

psi_det_size psi_det_sorted_bit psi_occ_pattern

h_apply_cisd_diexc:()

File : h_apply.irp.f_shell_8

subroutine H_apply_cisd_diexc(key_in, key_prev, hole_1,particl_1, hole_2, particl_2, fock_diag_tmp, i_generator, iproc_in  )

Needs:

n_int

n_det

mo_num

Called by:

h_apply_cisd()

Calls:

h_apply_cisd_diexcp()

h_apply_cisd_diexcorg:()

File : h_apply.irp.f_shell_8

subroutine H_apply_cisd_diexcOrg(key_in,key_mask,hole_1,particl_1,hole_2, particl_2, fock_diag_tmp, i_generator, iproc_in  )

Generate all double excitations of key_in using the bit masks of holes and particles. Assume N_int is already provided.

Needs:

n_int

elec_alpha_num

mo_num

Called by:

h_apply_cisd_diexcp()

Calls:

bitstring_to_list_ab()

fill_h_apply_buffer_no_selection()

h_apply_cisd_diexcp:()

File : h_apply.irp.f_shell_8

subroutine H_apply_cisd_diexcP(key_in, fs1, fh1, particl_1, fs2, fh2, particl_2, fock_diag_tmp, i_generator, iproc_in  )

Needs:

n_int

n_det

mo_num

Called by:

h_apply_cisd_diexc()

Calls:

h_apply_cisd_diexcorg()

h_apply_cisd_monoexc:()

File : h_apply.irp.f_shell_8

subroutine H_apply_cisd_monoexc(key_in, hole_1,particl_1,fock_diag_tmp,i_generator,iproc_in  )

Generate all single excitations of key_in using the bit masks of holes and particles. Assume N_int is already provided.

Needs:

n_int

elec_alpha_num

mo_num

Called by:

h_apply_cisd()

Calls:

bitstring_to_list_ab()

fill_h_apply_buffer_no_selection()