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quantum_package/plugins/Perturbation/Moller_plesset.irp.f
Thomas Applencourt 6a91e63cf3 Move into plugins
2015-06-17 18:23:56 +02:00

43 lines
1.5 KiB
Fortran

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