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https://github.com/LCPQ/quantum_package
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67 lines
2.4 KiB
Fortran
67 lines
2.4 KiB
Fortran
subroutine pt2_epstein_nesbet(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
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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 Epstein-Nesbet 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>/( E(i) - <det_pert|H|det_pert> )
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!
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! e_2_pert(i) = <psi(i)|H|det_pert>^2/( E(i) - <det_pert|H|det_pert> )
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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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double precision, parameter :: eps = tiny(1.d0)
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ASSERT (Nint == N_int)
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ASSERT (Nint > 0)
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call i_H_psi(det_pert,psi_ref,psi_ref_coef,Nint,ndet,psi_ref_size,n_st,i_H_psi_array)
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H_pert_diag = diag_H_mat_elem(det_pert,Nint)
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do i =1,n_st
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c_pert(i) = i_H_psi_array(i) / (reference_energy(i) - H_pert_diag + eps)
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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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subroutine pt2_epstein_nesbet_2x2(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
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double precision :: i_H_psi_array(N_st)
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BEGIN_DOC
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! compute the Epstein-Nesbet 2x2 diagonalization coefficient and energetic contribution
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!
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! for the various n_st states.
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!
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! e_2_pert(i) = 0.5 * (( <det_pert|H|det_pert> - E(i) ) - sqrt( ( <det_pert|H|det_pert> - E(i)) ^2 + 4 <psi(i)|H|det_pert>^2 )
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!
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! c_pert(i) = e_2_pert(i)/ <psi(i)|H|det_pert>
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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,delta_e
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double precision, parameter :: eps = tiny(1.d0)
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ASSERT (Nint == N_int)
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ASSERT (Nint > 0)
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call i_H_psi(det_pert,psi_ref,psi_ref_coef,Nint,N_det_ref,psi_ref_size,n_st,i_H_psi_array)
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H_pert_diag = diag_H_mat_elem(det_pert,Nint)
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do i =1,n_st
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delta_e = H_pert_diag - reference_energy(i)
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e_2_pert(i) = 0.5d0 * (delta_e - dsqrt(delta_e * delta_e + 4.d0 * i_H_psi_array(i) * i_H_psi_array(i)))
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c_pert(i) = e_2_pert(i)/(i_H_psi_array(i)+eps)
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enddo
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end
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