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84 lines
2.4 KiB
Fortran
84 lines
2.4 KiB
Fortran
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program cis
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implicit none
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BEGIN_DOC
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!
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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
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! occupancy, and performs all single excitations on top of it.
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! Disregarding spatial symmetry, it computes the `n_states` lowest
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! eigenstates of that CI matrix. (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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!
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! Ground state calculation
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! ------------------------
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!
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! To be sure to have the lowest |SCF| solution, perform an :ref:`scf`
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! (see the :ref:`hartree_fock` module), then a :ref:`cis`, save
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! the natural orbitals (see :ref:`save_natorb`) and re-run an
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! :ref:`scf` optimization from this |MO| guess.
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!
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!
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! Excited states calculations
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! ---------------------------
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!
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! The lowest excited states are much likely to be dominated by
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! single-excitations. Therefore, running a :ref:`cis` will save
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! the `n_states` lowest states within the |CIS| space in the |EZFIO|
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! directory, which can afterwards be used as guess wave functions for
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! a further multi-state |FCI| calculation if :option:`determinants read_wf`
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! is set to |true| before running the :ref:`fci`
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! executable.
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!
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!
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! If :option:`determinants s2_eig` is set to |true|, the |CIS|
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! will only retain states having the expected |S^2| value (see
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! :option:`determinants expected_s2`). Otherwise, the |CIS| will take
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! the lowest :option:`determinants n_states`, whatever multiplicity
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! they are.
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!
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! .. note::
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!
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! To discard some orbitals, use the :ref:`qp_set_mo_class`
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! command 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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!
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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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