quack/src/RPA/phACFDT.f90

subroutine phACFDT(exchange_kernel,dRPA,TDA,singlet,triplet,nBas,nC,nO,nV,nR,nS,ERI,e,EcAC)

! Compute the correlation energy via the adiabatic connection fluctuation dissipation theorem

  implicit none
  include 'parameters.h'
  include 'quadrature.h'

! Input variables

  logical,intent(in)            :: exchange_kernel
  logical,intent(in)            :: dRPA
  logical,intent(in)            :: TDA
  logical,intent(in)            :: singlet
  logical,intent(in)            :: triplet

  integer,intent(in)            :: nBas
  integer,intent(in)            :: nC
  integer,intent(in)            :: nO
  integer,intent(in)            :: nV
  integer,intent(in)            :: nR
  integer,intent(in)            :: nS
  double precision,intent(in)   :: e(nBas)
  double precision,intent(in)   :: ERI(nBas,nBas,nBas,nBas)

! Local variables

  integer                       :: ispin
  integer                       :: iAC
  double precision              :: lambda
  double precision,allocatable  :: Ec(:,:)

  double precision              :: EcRPA
  double precision,allocatable  :: Aph(:,:)
  double precision,allocatable  :: Bph(:,:)

  double precision,allocatable  :: Om(:)
  double precision,allocatable  :: XpY(:,:)
  double precision,allocatable  :: XmY(:,:)

! Output variables

  double precision,intent(out)  :: EcAC(nspin)

! Memory allocation

  allocate(Ec(nAC,nspin))
  allocate(Aph(nS,nS),Bph(nS,nS),Om(nS),XpY(nS,nS),XmY(nS,nS))

! Antisymmetrized kernel version

  if(exchange_kernel) then

    write(*,*)
    write(*,*) '*** Exchange kernel version ***'
    write(*,*)

  end if

  EcAC(:) = 0d0
  Ec(:,:) = 0d0

! Singlet manifold

  if(singlet) then

    ispin = 1

    write(*,*) '--------------'
    write(*,*) 'Singlet states'
    write(*,*) '--------------'
    write(*,*) 

    write(*,*) '-----------------------------------------------------------------------------------'
    write(*,'(2X,A15,1X,A30,1X,A30)') 'lambda','Ec(lambda)','Tr(K x P_lambda)'
    write(*,*) '-----------------------------------------------------------------------------------'

    do iAC=1,nAC
 
      lambda = rAC(iAC)

      call phLR_A(ispin,dRPA,nBas,nC,nO,nV,nR,nS,lambda,e,ERI,Aph)
      if(.not.TDA) call phLR_B(ispin,dRPA,nBas,nC,nO,nV,nR,nS,lambda,ERI,Bph)

      call phLR(TDA,nS,Aph,Bph,EcAc(ispin),Om,XpY,XmY)

      call phACFDT_correlation_energy(ispin,exchange_kernel,nBas,nC,nO,nV,nR,nS,ERI,XpY,XmY,Ec(iAC,ispin))

      write(*,'(2X,F15.6,1X,F30.15,1X,F30.15)') lambda,EcAC(ispin),Ec(iAC,ispin)

    end do

    EcAC(ispin) = 0.5d0*dot_product(wAC,Ec(:,ispin))

    if(exchange_kernel) EcAC(ispin) = 0.5d0*EcAC(ispin)

    write(*,*) '-----------------------------------------------------------------------------------'
    write(*,'(2X,A50,1X,F15.6)') ' Ec(AC) via Gauss-Legendre quadrature:',EcAC(ispin)
    write(*,*) '-----------------------------------------------------------------------------------'
    write(*,*)

  end if
 
! Triplet manifold

  if(triplet) then

    ispin = 2

    write(*,*) '--------------'
    write(*,*) 'Triplet states'
    write(*,*) '--------------'
    write(*,*) 

    write(*,*) '-----------------------------------------------------------------------------------'
    write(*,'(2X,A15,1X,A30,1X,A30)') 'lambda','Ec(lambda)','Tr(K x P_lambda)'
    write(*,*) '-----------------------------------------------------------------------------------'

    do iAC=1,nAC
 
      lambda = rAC(iAC)

      call phLR_A(ispin,dRPA,nBas,nC,nO,nV,nR,nS,lambda,e,ERI,Aph)
      if(.not.TDA) call phLR_B(ispin,dRPA,nBas,nC,nO,nV,nR,nS,lambda,ERI,Bph)

      call phLR(TDA,nS,Aph,Bph,EcAc(ispin),Om,XpY,XmY)

      call phACFDT_correlation_energy(ispin,exchange_kernel,nBas,nC,nO,nV,nR,nS,ERI,XpY,XmY,Ec(iAC,ispin))

      write(*,'(2X,F15.6,1X,F30.15,1X,F30.15)') lambda,EcAC(ispin),Ec(iAC,ispin)

    end do

    EcAC(ispin) = 0.5d0*dot_product(wAC,Ec(:,ispin))

    if(exchange_kernel) EcAC(ispin) = 1.5d0*EcAC(ispin)

    write(*,*) '-----------------------------------------------------------------------------------'
    write(*,'(2X,A50,1X,F15.6)') ' Ec(AC) via Gauss-Legendre quadrature:',EcAC(ispin)
    write(*,*) '-----------------------------------------------------------------------------------'
    write(*,*)

  end if

end subroutine