QuantumPackage/plugins/local/slater_tc_no_opt/slater_tc_slow.irp.f

! ---

subroutine htilde_mu_mat_bi_ortho_tot_slow(key_j, key_i, Nint, htot)

  BEGIN_DOC
  ! <key_j |H_tilde | key_i> where |key_j> is developed on the LEFT basis and |key_i> is developed on the RIGHT basis
  !!
  !! WARNING !!
  ! 
  ! Non hermitian !!
  END_DOC

  use bitmasks

  implicit none
  integer, intent(in)           :: Nint
  integer(bit_kind), intent(in) :: key_j(Nint,2),key_i(Nint,2)
  double precision, intent(out) :: htot
  double precision              :: hmono, htwoe, hthree
  integer :: degree

  call get_excitation_degree(key_j, key_i, degree, Nint)
  if(degree.gt.2) then
    htot = 0.d0
  else
    call htilde_mu_mat_bi_ortho_slow(key_j, key_i, Nint, hmono, htwoe, hthree, htot)
  endif

end

! --

subroutine htilde_mu_mat_bi_ortho_slow(key_j, key_i, Nint, hmono, htwoe, hthree, htot)

  BEGIN_DOC
  !
  ! <key_j |H_tilde | key_i> where |key_j> is developed on the LEFT basis and |key_i> is developed on the RIGHT basis
  !!
  ! Returns the detail of the matrix element in terms of single, two and three electron contribution. 
  !! WARNING !!
  ! 
  ! Non hermitian !!
  !
  END_DOC

  use bitmasks

  implicit none
  integer,           intent(in) :: Nint
  integer(bit_kind), intent(in) :: key_i(Nint,2), key_j(Nint,2)
  double precision, intent(out) :: hmono, htwoe, hthree, htot
  integer                       :: degree 

  hmono  = 0.d0
  htwoe  = 0.d0
  htot   = 0.d0
  hthree = 0.d0

  call get_excitation_degree(key_i, key_j, degree, Nint)
  if(degree.gt.2) return

  if(degree == 0) then
    call diag_htc_bi_orth_2e_brute(Nint, key_i, hmono, htwoe, htot)
  else if (degree == 1) then
    call single_htilde_mu_mat_bi_ortho_slow(Nint, key_j, key_i, hmono, htwoe, htot)
  else if(degree == 2) then
    call double_htilde_mu_mat_bi_ortho_slow(Nint, key_j, key_i, hmono, htwoe, htot)
  endif

  if(three_body_h_tc) then
    if(degree == 2) then
      if((.not.double_normal_ord) .and. (elec_num .gt. 2) .and. three_e_5_idx_term) then
        call double_htilde_three_body_ints_bi_ort_slow(Nint, key_j, key_i, hthree)
      endif
    else if((degree == 1) .and. (elec_num .gt. 2) .and. three_e_4_idx_term) then
      call single_htilde_three_body_ints_bi_ort_slow(Nint, key_j, key_i, hthree)
    else if((degree == 0) .and. (elec_num .gt. 2) .and. three_e_3_idx_term) then
      call diag_htc_bi_orth_3e_brute(Nint, key_i, hthree)
    endif
  endif

  htot = hmono + htwoe + hthree

  if(degree==0) then
    htot += nuclear_repulsion

    if(noL_standard) then
      PROVIDE noL_0e
      htot += noL_0e
    endif
  endif
 
end

! ---

subroutine double_htilde_mu_mat_bi_ortho_slow(Nint, key_j, key_i, hmono, htwoe, htot)

  BEGIN_DOC
  ! <key_j |H_tilde | key_i> for double excitation  ONLY FOR ONE- AND TWO-BODY TERMS 
  !!
  !! WARNING !!
  ! 
  ! Non hermitian !!
  END_DOC

  use bitmasks

  implicit none
  integer,           intent(in) :: Nint 
  integer(bit_kind), intent(in) :: key_j(Nint,2), key_i(Nint,2)
  double precision, intent(out) :: hmono, htwoe, htot
  integer                       :: occ(Nint*bit_kind_size,2)
  integer                       :: Ne(2), i, j, ii, jj, ispin, jspin, k, kk
  integer                       :: degree,exc(0:2,2,2)
  integer                       :: h1, p1, h2, p2, s1, s2
  integer                       :: other_spin(2)
  integer(bit_kind)             :: key_i_core(Nint,2)
  double precision              :: get_mo_two_e_integral_tc_int,phase

!  PROVIDE mo_two_e_integrals_tc_int_in_map mo_bi_ortho_tc_two_e

  other_spin(1) = 2
  other_spin(2) = 1

  call get_excitation_degree(key_i, key_j, degree, Nint)

  hmono = 0.d0
  htwoe= 0.d0
  htot = 0.d0

  if(degree.ne.2)then
   return
  endif

   call bitstring_to_list_ab(key_i, occ, Ne, Nint)
  call get_double_excitation(key_i, key_j, exc, phase, Nint)
  call decode_exc(exc, 2, h1, p1, h2, p2, s1, s2)

  if(s1.ne.s2)then
   ! opposite spin two-body 
!   key_j, key_i
    htwoe  = mo_bi_ortho_tc_two_e(p2,p1,h2,h1) 
    if(three_body_h_tc.and.double_normal_ord.and.+Ne(1).gt.2)then
     htwoe += normal_two_body_bi_orth(p2,h2,p1,h1)!!! WTF ???
    endif
  else
   ! same spin two-body 
   ! direct terms 
   htwoe  = mo_bi_ortho_tc_two_e(p2,p1,h2,h1)  
   ! exchange terms 
   htwoe -= mo_bi_ortho_tc_two_e(p1,p2,h2,h1) 
   if(three_body_h_tc.and.double_normal_ord.and.+Ne(1).gt.2)then
    htwoe -= normal_two_body_bi_orth(h2,p1,h1,p2)!!! WTF ???
    htwoe += normal_two_body_bi_orth(h1,p1,h2,p2)!!! WTF ???
   endif
  endif
  htwoe *= phase
  htot =  htwoe 

end


subroutine single_htilde_mu_mat_bi_ortho_slow(Nint, key_j, key_i, hmono, htwoe, htot)

  BEGIN_DOC
  ! <key_j |H_tilde | key_i> for single excitation ONLY FOR ONE- AND TWO-BODY TERMS 
  !!
  !! WARNING !!
  ! 
  ! Non hermitian !!
  END_DOC

  use bitmasks

  implicit none
  integer,           intent(in) :: Nint
  integer(bit_kind), intent(in) :: key_j(Nint,2), key_i(Nint,2)
  double precision, intent(out) :: hmono, htwoe, htot
  integer                       :: occ(Nint*bit_kind_size,2)
  integer                       :: Ne(2), i, j, ii, jj, ispin, jspin, k, kk
  integer                       :: degree,exc(0:2,2,2)
  integer                       :: h1, p1, h2, p2, s1, s2
  double precision              :: get_mo_two_e_integral_tc_int, phase
  double precision              :: direct_int, exchange_int_12, exchange_int_23, exchange_int_13
  integer                       :: other_spin(2)
  integer(bit_kind)             :: key_j_core(Nint,2), key_i_core(Nint,2)

!  PROVIDE mo_two_e_integrals_tc_int_in_map mo_bi_ortho_tc_two_e
!
!  PROVIDE core_bitmask core_fock_operator mo_integrals_erf_map


  other_spin(1) = 2
  other_spin(2) = 1

  hmono = 0.d0
  htwoe= 0.d0
  htot = 0.d0
  call get_excitation_degree(key_i, key_j, degree, Nint)
  if(degree.ne.1)then
   return
  endif
!  if(core_tc_op)then
!   print*,'core_tc_op not already taken into account for bi ortho'
!   print*,'stopping ...'
!   stop
!   do i = 1, Nint
!    key_i_core(i,1) = xor(key_i(i,1),core_bitmask(i,1))
!    key_i_core(i,2) = xor(key_i(i,2),core_bitmask(i,2))
!    key_j_core(i,1) = xor(key_j(i,1),core_bitmask(i,1))
!    key_j_core(i,2) = xor(key_j(i,2),core_bitmask(i,2))
!   enddo
!   call bitstring_to_list_ab(key_i_core, occ, Ne, Nint)
!  else
   call bitstring_to_list_ab(key_i, occ, Ne, Nint)
!  endif

  call get_single_excitation(key_i, key_j, exc, phase, Nint)
  call decode_exc(exc,1,h1,p1,h2,p2,s1,s2)
!  if(h1==14.and.p1==2)then
!   print*,'h1,p1 old = ',h1,p1
!  endif

  hmono = mo_bi_ortho_tc_one_e(p1,h1) * phase

!  if(core_tc_op)then
!   print*,'core_tc_op not already taken into account for bi ortho'
!   print*,'stopping ...'
!   stop
!   hmono += phase * core_fock_operator(h1,p1)
!  endif
  
   ! alpha/beta two-body 
   ispin = other_spin(s1)
   if(s1==1)then
    ! single alpha 
    do i = 1, Ne(ispin) ! electron 2 
     ii = occ(i,ispin) 
     htwoe += mo_bi_ortho_tc_two_e(ii,p1,ii,h1) 
    enddo
   else
    ! single beta 
    do i = 1, Ne(ispin) ! electron 1 
     ii = occ(i,ispin) 
     htwoe += mo_bi_ortho_tc_two_e(p1,ii,h1,ii) 
    enddo
   endif
!   ! same spin two-body 
   do i = 1, Ne(s1)
    ii = occ(i,s1) 
    ! (h1p1|ii ii) - (h1 ii| p1 ii)
    htwoe += mo_bi_ortho_tc_two_e(ii,p1,ii,h1) - mo_bi_ortho_tc_two_e(p1,ii,ii,h1) 
   enddo
   
  htwoe  *= phase
  htot = hmono + htwoe 

end