quantum_package/plugins/DavidsonDressed/diagonalize_CI.irp.f

BEGIN_PROVIDER [ double precision, CI_energy_dressed, (N_states_diag) ]
  implicit none
  BEGIN_DOC
  ! N_states lowest eigenvalues of the CI matrix
  END_DOC
  
  integer                        :: j
  character*(8)                  :: st
  call write_time(6)
  do j=1,min(N_det,N_states_diag)
    CI_energy_dressed(j) = CI_electronic_energy_dressed(j) + nuclear_repulsion
  enddo
  do j=1,min(N_det,N_states)
    write(st,'(I4)') j
    call write_double(6,CI_energy_dressed(j),'Energy of state '//trim(st))
    call write_double(6,CI_eigenvectors_s2_dressed(j),'S^2 of state '//trim(st))
  enddo

END_PROVIDER

 BEGIN_PROVIDER [ double precision, CI_electronic_energy_dressed, (N_states_diag) ]
&BEGIN_PROVIDER [ double precision, CI_eigenvectors_dressed, (N_det,N_states_diag) ]
&BEGIN_PROVIDER [ double precision, CI_eigenvectors_s2_dressed, (N_states_diag) ]
  BEGIN_DOC
  ! Eigenvectors/values of the CI matrix
  END_DOC
  implicit none
  double precision               :: ovrlp,u_dot_v
  integer                        :: i_good_state
  integer, allocatable           :: index_good_state_array(:)
  logical, allocatable           :: good_state_array(:)
  double precision, allocatable  :: s2_values_tmp(:)
  integer                        :: i_other_state
  double precision, allocatable  :: eigenvectors(:,:), eigenvectors_s2(:,:), eigenvalues(:)
  integer                        :: i_state
  double precision               :: e_0
  integer                        :: i,j,k,mrcc_state
  double precision, allocatable  :: s2_eigvalues(:)
  double precision, allocatable  :: e_array(:)
  integer, allocatable           :: iorder(:)

  PROVIDE threshold_davidson nthreads_davidson
  ! Guess values for the "N_states" states of the CI_eigenvectors_dressed
  do j=1,min(N_states,N_det)
    do i=1,N_det
      CI_eigenvectors_dressed(i,j) = psi_coef(i,j)
    enddo
  enddo

  do j=min(N_states,N_det)+1,N_states_diag
    do i=1,N_det
      CI_eigenvectors_dressed(i,j) = 0.d0
    enddo
  enddo

  if (diag_algorithm == "Davidson") then
    
    do j=1,min(N_states,N_det)
      do i=1,N_det
        CI_eigenvectors_dressed(i,j) = psi_coef(i,j)
      enddo
    enddo
    call davidson_diag_HS2(psi_det,CI_eigenvectors_dressed, CI_eigenvectors_s2_dressed,&
        size(CI_eigenvectors_dressed,1), CI_electronic_energy_dressed,&
        N_det,min(N_det,N_states),min(N_det,N_states_diag),N_int,1)
    call u_0_S2_u_0(CI_eigenvectors_s2_dressed,CI_eigenvectors_dressed,N_det,psi_det,N_int,&
        N_states_diag,size(CI_eigenvectors_dressed,1))
    
    
  else if (diag_algorithm == "Lapack") then
    
    allocate (eigenvectors(size(H_matrix_dressed,1),N_det))
    allocate (eigenvalues(N_det))

    call lapack_diag(eigenvalues,eigenvectors,                         &
        H_matrix_dressed,size(H_matrix_dressed,1),N_det)
     CI_electronic_energy_dressed(:) = 0.d0
     if (s2_eig) then
       i_state = 0
       allocate (s2_eigvalues(N_det))
       allocate(index_good_state_array(N_det),good_state_array(N_det))
       good_state_array = .False.

       call u_0_S2_u_0(s2_eigvalues,eigenvectors,N_det,psi_det,N_int,&
                  N_det,size(eigenvectors,1))
       do j=1,N_det
         ! Select at least n_states states with S^2 values closed to "expected_s2"
         if(dabs(s2_eigvalues(j)-expected_s2).le.0.5d0)then
           i_state +=1
           index_good_state_array(i_state) = j
           good_state_array(j) = .True.
         endif
         if(i_state.eq.N_states) then
           exit
         endif
       enddo
       if(i_state .ne.0)then
         ! Fill the first "i_state" states that have a correct S^2 value
         do j = 1, i_state
           do i=1,N_det
             CI_eigenvectors_dressed(i,j) = eigenvectors(i,index_good_state_array(j))
           enddo
           CI_electronic_energy_dressed(j) = eigenvalues(index_good_state_array(j))
           CI_eigenvectors_s2_dressed(j) = s2_eigvalues(index_good_state_array(j))
         enddo
         i_other_state = 0
         do j = 1, N_det
           if(good_state_array(j))cycle
           i_other_state +=1
           if(i_state+i_other_state.gt.n_states_diag)then
             exit
           endif
           do i=1,N_det
             CI_eigenvectors_dressed(i,i_state+i_other_state) = eigenvectors(i,j)
           enddo
           CI_electronic_energy_dressed(i_state+i_other_state) = eigenvalues(j)
           CI_eigenvectors_s2_dressed(i_state+i_other_state) = s2_eigvalues(i_state+i_other_state)
         enddo
       else
         print*,''
         print*,'!!!!!!!!   WARNING  !!!!!!!!!'
         print*,'  Within the ',N_det,'determinants selected'
         print*,'  and the ',N_states_diag,'states requested'
         print*,'  We did not find any state with S^2 values close to ',expected_s2
         print*,'  We will then set the first N_states eigenvectors of the H matrix'
         print*,'  as the CI_eigenvectors_dressed'
         print*,'  You should consider more states and maybe ask for s2_eig to be .True. or just enlarge the CI space'
         print*,''
         do j=1,min(N_states_diag,N_det)
           do i=1,N_det
             CI_eigenvectors_dressed(i,j) = eigenvectors(i,j)
           enddo
           CI_electronic_energy_dressed(j) = eigenvalues(j)
           CI_eigenvectors_s2_dressed(j) = s2_eigvalues(j)
         enddo
       endif
       deallocate(index_good_state_array,good_state_array)
       deallocate(s2_eigvalues)
     else
       call u_0_S2_u_0(CI_eigenvectors_s2_dressed,eigenvectors,N_det,psi_det,N_int,&
          min(N_det,N_states_diag),size(eigenvectors,1))
       ! Select the "N_states_diag" states of lowest energy
       do j=1,min(N_det,N_states_diag)
         do i=1,N_det
           CI_eigenvectors_dressed(i,j) = eigenvectors(i,j)
         enddo
         CI_electronic_energy_dressed(j) = eigenvalues(j)
       enddo
     endif
    deallocate(eigenvectors,eigenvalues)
  endif

END_PROVIDER

subroutine diagonalize_CI_dressed
  implicit none
  BEGIN_DOC
!  Replace the coefficients of the CI states by the coefficients of the 
!  eigenstates of the CI matrix
  END_DOC
  integer :: i,j
  do j=1,N_states
    do i=1,N_det
      psi_coef(i,j) = CI_eigenvectors_dressed(i,j)
    enddo
  enddo
  SOFT_TOUCH psi_coef 
end



BEGIN_PROVIDER [ double precision, h_matrix_dressed, (N_det,N_det) ]
 implicit none
 BEGIN_DOC
 ! Dressed H with Delta_ij
 END_DOC
 integer                        :: i, j, k

  h_matrix_dressed(1:N_det,1:N_det) = h_matrix_all_dets(1:N_det,1:N_det)
  do k=1,N_states
    do j=1,N_det
      do i=1,N_det
        h_matrix_dressed(i,j) = h_matrix_dressed(i,j) +             &
            0.5d0 * (dressing_column_h(i,k) * psi_coef(j,k) + &
                     dressing_column_h(j,k) * psi_coef(i,k))
      enddo
    enddo
  enddo

END_PROVIDER