mirror of https://github.com/pfloos/quack
108 lines
2.9 KiB
Fortran
108 lines
2.9 KiB
Fortran
function GF12Int(ExpG,ExpA,CenterA,AngMomA,ExpB,CenterB,AngMomB,ExpC,CenterC,AngMomC,ExpD,CenterD,AngMomD)
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! Compute two-electron integrals over Gaussian geminals
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implicit none
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! Input variables
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double precision,intent(in) :: ExpG
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double precision,intent(in) :: ExpA,ExpB,ExpC,ExpD
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double precision,intent(in) :: CenterA(3),CenterB(3),CenterC(3),CenterD(3)
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integer,intent(in) :: AngMomA(3),AngMomB(3),AngMomC(3),AngMomD(3)
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! Local variables
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double precision :: ExpAi,ExpBi,ExpCi,ExpDi,ExpGi
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double precision :: ExpP,ExpQ,ExpPi,ExpQi,ExpPGQi
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double precision :: CenterP(3),CenterQ(3),CenterAB(3),CenterCD(3),CenterPQSq(3),CenterRA(3),CenterRC(3)
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double precision :: NormABSq,NormCDSq
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double precision :: GAB,GCD
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double precision :: fP,fG,fQ,gP,gG,gQ
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double precision :: HRRF12
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integer :: i
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double precision :: pi
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double precision :: start_RR,finish_RR,t_RR
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double precision :: Gabcd(3)
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! Output variables
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double precision :: GF12Int
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pi = 4d0*atan(1d0)
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! Pre-computed shell quantities
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ExpAi = 1d0/ExpA
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ExpBi = 1d0/ExpB
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ExpCi = 1d0/ExpC
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ExpDi = 1d0/ExpD
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ExpGi = 1d0/ExpG
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! Pre-computed quantities for shell-pair AB
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ExpP = ExpA + ExpB
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ExpPi = 1d0/ExpP
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NormABSq = 0d0
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Do i=1,3
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CenterP(i) = (ExpA*CenterA(i) + ExpB*CenterB(i))*ExpPi
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CenterAB(i) = CenterA(i) - CenterB(i)
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NormABSq = NormABSq + CenterAB(i)**2
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Enddo
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GAB = (pi*ExpPi)**(1.5d0)*exp(-NormABSq/(ExpAi+ExpBi))
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! Pre-computed quantities for shell-pair CD
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ExpQ = ExpC + ExpD
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ExpQi = 1d0/ExpQ
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NormCDSq = 0d0
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Do i=1,3
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CenterQ(i) = (ExpC*CenterC(i) + ExpD*CenterD(i))*ExpQi
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CenterCD(i) = CenterC(i) - CenterD(i)
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NormCDSq = NormCDSq + CenterCD(i)**2
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Enddo
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GCD = (pi*ExpQi)**(1.5d0)*exp(-NormCDSq/(ExpCi+ExpDi))
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! Pre-computed shell-quartet quantities
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ExpPGQi = ExpPi + ExpGi + ExpQi
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Do i=1,3
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CenterPQSq(i) = (CenterP(i) - CenterQ(i))**2
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Enddo
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fP = ExpPi/ExpPGQi
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fG = ExpGi/ExpPGQi
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fQ = ExpQi/ExpPGQi
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gP = (1d0 - fP)*0.5d0*ExpPi
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gG = fP*0.5d0*expQi
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gQ = (1d0 - fQ)*0.5d0*ExpQi
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do i=1,3
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CenterRA(i) = CenterP(i) - CenterA(i) + fP*(CenterQ(i) - CenterP(i))
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CenterRC(i) = CenterQ(i) - CenterC(i) + fQ*(CenterP(i) - CenterQ(i))
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enddo
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!------------------------------------------------------------------------
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! Launch reccurence relations!
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!------------------------------------------------------------------------
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call cpu_time(start_RR)
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! Loop over cartesian directions
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Do i=1,3
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Gabcd(i) = HRRF12(AngMomA(i),AngMomB(i),AngMomC(i),AngMomD(i),fG,gP,gG,gQ,ExpPGQi, &
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CenterPQSq(i),CenterRA(i),CenterRC(i),CenterAB(i),CenterCD(i))
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Enddo
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call cpu_time(finish_RR)
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! Print result
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GF12Int = GAB*GCD*Gabcd(1)*Gabcd(2)*Gabcd(3)
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t_RR = finish_RR - start_RR
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end function GF12Int
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