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qp2/src/cis_read/cis_read.irp.f
Anthony Scemama 57b47807fa
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Added CIS_read
2022-04-21 14:27:36 +02:00

89 lines
2.5 KiB
Fortran

program cis
implicit none
BEGIN_DOC
!
! 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 :option:`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 :ref:`scf`
! (see the :ref:`module_hartree_fock` module), then a :ref:`cis`, save the
! natural orbitals (see :ref:`save_natorb`) and re-run an :ref:`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 :ref:`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 :option:`determinants
! read_wf` is set to |true| before running the :ref:`fci` executable.
!
!
! If :option:`determinants s2_eig` is set to |true|, the |CIS|
! will only retain states having the expected |S^2| value (see
! :option:`determinants expected_s2`). Otherwise, the |CIS| will take
! the lowest :option:`determinants n_states`, whatever multiplicity
! they are.
!
! .. note::
!
! To discard some orbitals, use the :ref:`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
!
END_DOC
read_wf = .True.
TOUCH read_wf
call run
end
subroutine run
implicit none
integer :: i
if(pseudo_sym)then
call H_apply_cis_sym
else
call H_apply_cis
endif
print*,''
print *, 'N_det = ', N_det
print*,'******************************'
print *, 'Energies of the states:'
do i = 1,N_states
print *, i, CI_energy(i)
enddo
if (N_states > 1) then
print*,''
print*,'******************************************************'
print*,'Excitation energies (au) (eV)'
do i = 2, N_states
print*, i ,CI_energy(i) - CI_energy(1), (CI_energy(i) - CI_energy(1))/0.0367502d0
enddo
print*,''
endif
call ezfio_set_cis_energy(CI_energy)
psi_coef = ci_eigenvectors
SOFT_TOUCH psi_coef
call save_wavefunction_truncated(save_threshold)
end