2019-09-14 14:15:25 +02:00
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subroutine MP2(nBas,nC,nR,ERI,ENuc,EHF,e,EcMP2)
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2019-09-09 16:51:15 +02:00
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! Perform third-order Moller-Plesset calculation
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implicit none
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! Input variables
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2019-09-14 14:15:25 +02:00
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integer,intent(in) :: nBas,nC,nR
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2019-09-09 16:51:15 +02:00
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double precision,intent(in) :: ENuc,EHF
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double precision,intent(in) :: ERI(nBas,nBas,nBas,nBas),e(nBas)
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! Local variables
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integer :: i,j,a,b
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double precision :: eps,E2a,E2b
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! Output variables
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double precision,intent(out) :: EcMP2(3)
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! Hello world
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write(*,*)
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write(*,*)'************************************************'
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write(*,*)'| Moller-Plesset second-order calculation |'
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write(*,*)'************************************************'
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write(*,*)
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! Compute MP2 energy
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E2a = 0d0
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E2b = 0d0
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2019-09-14 14:15:25 +02:00
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do i=nC+1,spin_occ_num
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do j=nC+1,spin_occ_num
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do a=spin_occ_num+1,nBas-nR
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do b=spin_occ_num+1,nBas-nR
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2019-09-09 16:51:15 +02:00
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eps = e(i) + e(j) - e(a) - e(b)
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! Second-order ring diagram
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E2a = E2a + ERI(i,j,a,b)*ERI(i,j,a,b)/eps
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! Second-order exchange diagram
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E2b = E2b + ERI(i,j,a,b)*ERI(i,j,b,a)/eps
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enddo
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enddo
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enddo
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enddo
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EcMP2(2) = 2d0*E2a
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EcMP2(3) = -E2b
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EcMP2(1) = EcMP2(2) + EcMP2(3)
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write(*,*)
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write(*,'(A32)') '-----------------------'
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write(*,'(A32)') ' MP2 calculation '
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write(*,'(A32)') '-----------------------'
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write(*,'(A32,1X,F16.10)') ' MP2 correlation energy',EcMP2(1)
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write(*,'(A32,1X,F16.10)') ' Direct part ',EcMP2(2)
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write(*,'(A32,1X,F16.10)') ' Exchange part ',EcMP2(3)
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write(*,'(A32)') '-----------------------'
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write(*,'(A32,1X,F16.10)') ' MP2 electronic energy',EHF + EcMP2(1)
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write(*,'(A32,1X,F16.10)') ' MP2 total energy',ENuc + EHF + EcMP2(1)
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write(*,'(A32)') '-----------------------'
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write(*,*)
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end subroutine MP2
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