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https://github.com/LCPQ/quantum_package
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51 lines
1.8 KiB
Fortran
51 lines
1.8 KiB
Fortran
subroutine pt2_moller_plesset(det_pert,c_pert,e_2_pert,H_pert_diag,Nint,ndet,n_st)
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use bitmasks
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implicit none
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integer, intent(in) :: Nint,ndet,n_st
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integer(bit_kind), intent(in) :: det_pert(Nint,2)
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double precision , intent(out) :: c_pert(n_st),e_2_pert(n_st),H_pert_diag(N_st)
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double precision :: i_H_psi_array(N_st)
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BEGIN_DOC
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! compute the standard Moller-Plesset perturbative first order coefficient and second order energetic contribution
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!
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! for the various n_st states.
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!
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! c_pert(i) = <psi(i)|H|det_pert>/(difference of orbital energies)
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!
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! e_2_pert(i) = <psi(i)|H|det_pert>^2/(difference of orbital energies)
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!
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END_DOC
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integer :: i,j
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double precision :: diag_H_mat_elem
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integer :: exc(0:2,2,2)
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integer :: degree
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double precision :: phase,delta_e,h
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integer :: h1,h2,p1,p2,s1,s2
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ASSERT (Nint == N_int)
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ASSERT (Nint > 0)
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call get_excitation(ref_bitmask,det_pert,exc,degree,phase,Nint)
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if (degree == 2) then
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call decode_exc(exc,degree,h1,p1,h2,p2,s1,s2)
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delta_e = Fock_matrix_diag_mo(h1) + Fock_matrix_diag_mo(h2) - &
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(Fock_matrix_diag_mo(p1) + Fock_matrix_diag_mo(p2))
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delta_e = 1.d0/delta_e
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else if (degree == 1) then
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call decode_exc(exc,degree,h1,p1,h2,p2,s1,s2)
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delta_e = Fock_matrix_diag_mo(h1) - Fock_matrix_diag_mo(p1)
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delta_e = 1.d0/delta_e
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else
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delta_e = 0.d0
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endif
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call i_H_psi(det_pert,psi_selectors,psi_selectors_coef,Nint,N_det,psi_selectors_size,n_st,i_H_psi_array)
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h = diag_H_mat_elem(det_pert,Nint)
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do i =1,n_st
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H_pert_diag(i) = h
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c_pert(i) = i_H_psi_array(i) *delta_e
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e_2_pert(i) = c_pert(i) * i_H_psi_array(i)
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enddo
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end
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