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https://github.com/LCPQ/quantum_package
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74 lines
2.4 KiB
Fortran
74 lines
2.4 KiB
Fortran
program cis
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implicit none
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BEGIN_DOC
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! Configuration Interaction with Single excitations.
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!
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! This program takes a reference Slater determinant of ROHF-like occupancy,
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!
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! and performs all single excitations on top of it, disregarding spatial
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! symmetry and compute the "n_states" lowest eigenstates of that CI matrix.
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! (see :option:`determinants n_states`)
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!
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! This program can be useful in many cases:
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!
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! * GROUND STATE CALCULATION: to be sure to have the lowest scf solution,
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! perform an :c:func:`scf` (see the :ref:`hartree_fock` module), then a :c:func:`cis`,
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! save the natural orbitals (see :c:func:`save_natorb`) and reperform an :c:func:`scf`
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! optimization from this MO guess
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!
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!
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!
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!
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! * EXCITED STATES CALCULATIONS: the lowest excited states are much likely to
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! be dominanted by single-excitations.
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! Therefore, running a :c:func:`cis` will save the "n_states" lowest states within
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! the CIS space
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! in the EZFIO folder, which can afterward be used as guess wave functions
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! for a further multi-state fci calculation if you specify "read_wf" = True
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! before running the fci executable (see :option:`determinants read_wf`).
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! Also, if you specify "s2_eig" = True, the cis will only retain states
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! having the good value :math:`S^2` value (see :option:`determinants
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! s2_eig` and :option:`determinants expected_s2`).
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! If "s2_eig" = False, it will take the lowest n_states, whatever multiplicity they are.
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!
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!
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!
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! Note: if you would like to discard some orbitals, use :ref:`qp_set_mo_class` to specify:
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!
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! * "core" orbitals which will be always doubly occupied
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!
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! * "act" orbitals where an electron can be either excited from or to
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!
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! * "del" orbitals which will be never occupied
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END_DOC
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read_wf = .False.
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SOFT_TOUCH read_wf
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call run
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end
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subroutine run
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implicit none
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integer :: i
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call H_apply_cis
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print *, 'N_det = ', N_det
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print*,'******************************'
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print *, 'Energies of the states:'
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do i = 1,N_states
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print *, i, CI_energy(i)
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enddo
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if (N_states > 1) then
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print*,'******************************'
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print*,'Excitation energies '
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do i = 2, N_states
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print*, i ,CI_energy(i) - CI_energy(1)
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enddo
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endif
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call ezfio_set_cis_energy(CI_energy)
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psi_coef = ci_eigenvectors
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SOFT_TOUCH psi_coef
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call save_wavefunction
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end
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