CIS(1)

NAME
cis - | Quantum Package > Configuration Interaction with Single excitations.

This program takes a reference Slater determinant of ROHF-like occupancy, and performs all single excitations on top of it. Disregarding spatial symmetry, it computes the n_states lowest eigenstates of that CI matrix. (see determinants n_states)

This program can be useful in many cases:

1.  Ground state calculation

    To be sure to have the lowest SCF solution, perform an scf (see the module_hartree_fock module), then a cis, save the natural orbitals (see save_natorb) and re-run an scf optimization from this MO guess.

2.  Excited states calculations

    The lowest excited states are much likely to be dominated by single-excitations. Therefore, running a cis will save the n_states lowest states within the CIS space in the EZFIO directory, which can afterwards be used as guess wave functions for a further multi-state FCI calculation if determinants read_wf is set to true before running the fci executable.

    If determinants s2_eig is set to true, the CIS will only retain states having the expected \widehat{S^2} value (see determinants expected_s2). Otherwise, the CIS will take the lowest determinants n_states, whatever multiplicity they are.

    NOTE: To discard some orbitals, use the qp_set_mo_class command to specify:

•   core orbitals which will be always doubly occupied

•   act orbitals where an electron can be either excited from or to

•   del orbitals which will be never occupied

    Needs:

•   read_wf

    Calls:

•   run()

    Touches:

•   fock_matrix_ao_alpha

•   fock_matrix_ao_alpha

•   mo_coef

•   level_shift

•   mo_coef

•   read_wf

AUTHOR
A. Scemama, E. Giner

COPYRIGHT
2019, A. Scemama, E. Giner