QuAcK/src/MBPT/qsGW.f90

subroutine qsGW(maxSCF,thresh,max_diis,doACFDT,exchange_kernel,doXBS,COHSEX,SOSEX,BSE,TDA_W,TDA,   & 
                G0W,GW0,dBSE,dTDA,evDyn,singlet,triplet,eta,nBas,nC,nO,nV,nR,nS,ENuc,ERHF,S,X,T,V, & 
                Hc,ERI_AO_basis,ERI_MO_basis,dipole_int,PHF,cHF,eHF)

! Perform a quasiparticle self-consistent GW calculation

  implicit none
  include 'parameters.h'

! Input variables

  integer,intent(in)            :: maxSCF
  integer,intent(in)            :: max_diis
  double precision,intent(in)   :: thresh
  logical,intent(in)            :: doACFDT
  logical,intent(in)            :: exchange_kernel
  logical,intent(in)            :: doXBS
  logical,intent(in)            :: COHSEX
  logical,intent(in)            :: SOSEX
  logical,intent(in)            :: BSE
  logical,intent(in)            :: TDA_W
  logical,intent(in)            :: TDA
  logical,intent(in)            :: dBSE
  logical,intent(in)            :: dTDA
  logical,intent(in)            :: evDyn
  logical,intent(in)            :: G0W
  logical,intent(in)            :: GW0
  logical,intent(in)            :: singlet
  logical,intent(in)            :: triplet
  double precision,intent(in)   :: eta
  integer,intent(in)            :: nBas,nC,nO,nV,nR,nS
  double precision,intent(in)   :: ENuc
  double precision,intent(in)   :: ERHF
  double precision,intent(in)   :: eHF(nBas)
  double precision,intent(in)   :: cHF(nBas,nBas)
  double precision,intent(in)   :: PHF(nBas,nBas)
  double precision,intent(in)   :: S(nBas,nBas)
  double precision,intent(in)   :: T(nBas,nBAs)
  double precision,intent(in)   :: V(nBas,nBas)
  double precision,intent(in)   :: Hc(nBas,nBas)
  double precision,intent(in)   :: X(nBas,nBas)
  double precision,intent(in)   :: ERI_AO_basis(nBas,nBas,nBas,nBas)
  double precision,intent(inout):: ERI_MO_basis(nBas,nBas,nBas,nBas)
  double precision,intent(in)   :: dipole_int(nBas,nBas,ncart)

! Local variables

  integer                       :: nSCF
  integer                       :: nBasSq
  integer                       :: ispin
  integer                       :: n_diis
  double precision              :: EqsGW
  double precision              :: EcRPA
  double precision              :: EcBSE(nspin)
  double precision              :: EcAC(nspin)
  double precision              :: EcGM
  double precision              :: Conv
  double precision              :: rcond
  double precision,external     :: trace_matrix
  double precision,allocatable  :: error_diis(:,:)
  double precision,allocatable  :: F_diis(:,:)
  double precision,allocatable  :: OmRPA(:)
  double precision,allocatable  :: XpY_RPA(:,:)
  double precision,allocatable  :: XmY_RPA(:,:)
  double precision,allocatable  :: rho_RPA(:,:,:)
  double precision,allocatable  :: c(:,:)
  double precision,allocatable  :: cp(:,:)
  double precision,allocatable  :: eGW(:)
  double precision,allocatable  :: P(:,:)
  double precision,allocatable  :: F(:,:)
  double precision,allocatable  :: Fp(:,:)
  double precision,allocatable  :: J(:,:)
  double precision,allocatable  :: K(:,:)
  double precision,allocatable  :: SigC(:,:)
  double precision,allocatable  :: SigCp(:,:)
  double precision,allocatable  :: SigCm(:,:)
  double precision,allocatable  :: Z(:)
  double precision,allocatable  :: error(:,:)

! Hello world

  write(*,*)
  write(*,*)'************************************************'
  write(*,*)'|       Self-consistent qsGW calculation       |'
  write(*,*)'************************************************'
  write(*,*)

! Warning 

  write(*,*) '!! ERIs in MO basis will be overwritten in qsGW !!'
  write(*,*)

! Stuff 

  nBasSq = nBas*nBas

! SOSEX correction

  if(SOSEX) then 
    write(*,*) 'SOSEX correction activated but BUG!'
    stop
  end if

! COHSEX approximation

  if(COHSEX) then 
    write(*,*) 'COHSEX approximation activated!'
    write(*,*)
  end if

! TDA for W

  if(TDA_W) then 
    write(*,*) 'Tamm-Dancoff approximation for dynamic screening!'
    write(*,*)
  end if

! TDA 

  if(TDA) then 
    write(*,*) 'Tamm-Dancoff approximation activated!'
    write(*,*)
  end if

! Memory allocation

  allocate(eGW(nBas),c(nBas,nBas),cp(nBas,nBas),P(nBas,nBas),F(nBas,nBas),Fp(nBas,nBas),        &
           J(nBas,nBas),K(nBas,nBas),SigC(nBas,nBas),SigCp(nBas,nBas),SigCm(nBas,nBas),Z(nBas), & 
           OmRPA(nS),XpY_RPA(nS,nS),XmY_RPA(nS,nS),rho_RPA(nBas,nBas,nS),                       &
           error(nBas,nBas),error_diis(nBasSq,max_diis),F_diis(nBasSq,max_diis))

! Initialization
  
  nSCF            = 0
  n_diis          = 0
  ispin           = 1
  Conv            = 1d0
  P(:,:)          = PHF(:,:)
  eGW(:)          = eHF(:)
  c(:,:)          = cHF(:,:)
  F_diis(:,:)     = 0d0
  error_diis(:,:) = 0d0

!------------------------------------------------------------------------
! Main loop
!------------------------------------------------------------------------

  do while(Conv > thresh .and. nSCF <= maxSCF)

    ! Buid Coulomb matrix

    call Coulomb_matrix_AO_basis(nBas,P,ERI_AO_basis,J)

    ! Compute exchange part of the self-energy 

    call exchange_matrix_AO_basis(nBas,P,ERI_AO_basis,K)

    ! AO to MO transformation of two-electron integrals

    call AOtoMO_integral_transform(1,1,1,1,nBas,c,ERI_AO_basis,ERI_MO_basis)

    ! Compute linear response

    if(.not. GW0 .or. nSCF == 0) then

      call linear_response(ispin,.true.,TDA_W,.false.,eta,nBas,nC,nO,nV,nR,nS,1d0,eGW,ERI_MO_basis, &
                           OmRPA,rho_RPA,EcRPA,OmRPA,XpY_RPA,XmY_RPA)

    endif

    ! Compute correlation part of the self-energy 

    call excitation_density(nBas,nC,nO,nR,nS,ERI_MO_basis,XpY_RPA,rho_RPA)

    if(G0W) then

      call self_energy_correlation(COHSEX,eta,nBas,nC,nO,nV,nR,nS,eHF,OmRPA,rho_RPA,EcGM,SigC)
      call renormalization_factor(COHSEX,eta,nBas,nC,nO,nV,nR,nS,eHF,OmRPA,rho_RPA,Z)

     else

      call self_energy_correlation(COHSEX,eta,nBas,nC,nO,nV,nR,nS,eGW,OmRPA,rho_RPA,EcGM,SigC)
      call renormalization_factor(COHSEX,eta,nBas,nC,nO,nV,nR,nS,eGW,OmRPA,rho_RPA,Z)

     endif

    ! Make correlation self-energy Hermitian and transform it back to AO basis
   
    SigCp = 0.5d0*(SigC + transpose(SigC))
    SigCm = 0.5d0*(SigC - transpose(SigC))

    call MOtoAO_transform(nBas,S,c,SigCp)
 
    ! Solve the quasi-particle equation

    F(:,:) = Hc(:,:) + J(:,:) + 0.5d0*K(:,:) + SigCp(:,:)

    ! Compute commutator and convergence criteria

    error = matmul(F,matmul(P,S)) - matmul(matmul(S,P),F)
    Conv = maxval(abs(error))

    ! DIIS extrapolation 

    n_diis = min(n_diis+1,max_diis)
    call DIIS_extrapolation(rcond,nBasSq,nBasSq,n_diis,error_diis,F_diis,error,F)

!   Reset DIIS if required

    if(abs(rcond) < 1d-15) n_diis = 0

    ! Diagonalize Hamiltonian in AO basis

    Fp = matmul(transpose(X),matmul(F,X))
    cp(:,:) = Fp(:,:)
    call diagonalize_matrix(nBas,cp,eGW)
    c = matmul(X,cp)

    ! Compute new density matrix in the AO basis

    P(:,:) = 2d0*matmul(c(:,1:nO),transpose(c(:,1:nO)))

    ! Print results

!   call print_excitation('RPA   ',ispin,nS,Omega(:,ispin))
    call print_qsGW(nBas,nO,nSCF,Conv,thresh,eHF,eGW,c,ENuc,P,T,V,Hc,J,K,F,SigCp,Z,EcRPA,EcGM,EqsGW)

    ! Increment

    nSCF = nSCF + 1

  enddo
!------------------------------------------------------------------------
! End main loop
!------------------------------------------------------------------------

! Compute second-order correction of the Hermitization error

! call qsGW_PT(nBas,nC,nO,nV,nR,nS,eGW,SigCm)

! Compute the overlap between HF and GW orbitals

! call overlap(nBas,cHF,c)

! Compute natural orbitals and occupancies

! call natural_orbital(nBas,nO,cHF,c)

! Did it actually converge?

  if(nSCF == maxSCF+1) then

    write(*,*)
    write(*,*)'!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!'
    write(*,*)'                 Convergence failed                 '
    write(*,*)'!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!'
    write(*,*)

    stop

  endif

! Deallocate memory

  deallocate(c,cp,P,F,Fp,J,K,SigC,SigCp,SigCm,Z,OmRPA,XpY_RPA,XmY_RPA,rho_RPA,error,error_diis,F_diis)

! Perform BSE calculation

  if(BSE) then

    call Bethe_Salpeter(TDA_W,TDA,dBSE,dTDA,evDyn,singlet,triplet,eta,nBas,nC,nO,nV,nR,nS,ERI_MO_basis,dipole_int, & 
                        eGW,eGW,EcBSE)

    if(exchange_kernel) then

      EcBSE(1) = 0.5d0*EcBSE(1)
      EcBSE(2) = 1.5d0*EcBSE(2)

    end if

    write(*,*)
    write(*,*)'-------------------------------------------------------------------------------'
    write(*,'(2X,A50,F20.10)') 'Tr@BSE@qsGW correlation energy (singlet) =',EcBSE(1)
    write(*,'(2X,A50,F20.10)') 'Tr@BSE@qsGW correlation energy (triplet) =',EcBSE(2)
    write(*,'(2X,A50,F20.10)') 'Tr@BSE@qsGW correlation energy           =',EcBSE(1) + EcBSE(2)
    write(*,'(2X,A50,F20.10)') 'Tr@BSE@qsGW total energy                 =',ENuc + EqsGW + EcBSE(1) + EcBSE(2)
    write(*,*)'-------------------------------------------------------------------------------'
    write(*,*)

!   Compute the BSE correlation energy via the adiabatic connection 

    if(doACFDT) then

      write(*,*) '------------------------------------------------------'
      write(*,*) 'Adiabatic connection version of BSE correlation energy'
      write(*,*) '------------------------------------------------------'
      write(*,*)

      if(doXBS) then

        write(*,*) '*** scaled screening version (XBS) ***'
        write(*,*)

      end if

      call ACFDT(exchange_kernel,doXBS,.true.,TDA_W,TDA,BSE,singlet,triplet,eta,nBas,nC,nO,nV,nR,nS,ERI_MO_basis,eGW,eGW,EcAC)

      write(*,*)
      write(*,*)'-------------------------------------------------------------------------------'
      write(*,'(2X,A50,F20.10)') 'AC@BSE@qsGW correlation energy (singlet) =',EcAC(1)
      write(*,'(2X,A50,F20.10)') 'AC@BSE@qsGW correlation energy (triplet) =',EcAC(2)
      write(*,'(2X,A50,F20.10)') 'AC@BSE@qsGW correlation energy           =',EcAC(1) + EcAC(2)
      write(*,'(2X,A50,F20.10)') 'AC@BSE@qsGW total energy                 =',ENuc + EqsGW + EcAC(1) + EcAC(2)
      write(*,*)'-------------------------------------------------------------------------------'
      write(*,*)

    end if

  end if

end subroutine qsGW