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https://github.com/pfloos/quack
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101 lines
2.0 KiB
Fortran
101 lines
2.0 KiB
Fortran
subroutine CC_B88_gga_exchange_energy(nEns,wEns,nCC,aCC,nGrid,weight,&
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rho,drho,Cx_choice,Ex)
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! Compute the unrestricted version of the curvature-corrected exchange functional
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implicit none
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include 'parameters.h'
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! Input variables
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integer,intent(in) :: nEns
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double precision,intent(in) :: wEns(nEns)
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integer,intent(in) :: nCC
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double precision,intent(in) :: aCC(nCC,nEns-1)
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integer,intent(in) :: nGrid
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double precision,intent(in) :: weight(nGrid)
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double precision,intent(in) :: rho(nGrid)
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double precision,intent(in) :: drho(3,nGrid)
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integer,intent(in) :: Cx_choice
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! Local variables
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integer :: iG
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double precision :: b
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double precision :: r,g,x
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double precision :: a1,b1,c1,d1,w1
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double precision :: a2,b2,c2,d2,w2
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double precision :: Fx1,Fx2,Cx
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! Output variables
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double precision :: Ex
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! Coefficients for B88 GGA exchange functional
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b = 0.0042d0
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! Defining enhancements factor for weight-dependent functionals
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! Parameters for first state
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a1 = aCC(1,1)
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b1 = aCC(2,1)
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c1 = aCC(3,1)
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d1 = aCC(4,1)
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! Parameters for second state
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a2 = aCC(1,2)
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b2 = aCC(2,2)
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c2 = aCC(3,2)
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d2 = aCC(4,2)
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w1 = wEns(2)
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Fx1 = 1d0 + a1*w1 + b1*w1**2 + c1*w1**3 + d1*w1**4
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w2 = wEns(3)
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Fx2 = 1d0 + a2*w2 + b2*w2**2 + c2*w2**3 + d2*w2**4
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select case (Cx_choice)
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case(1)
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Cx = Fx1
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case(2)
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Cx = Fx2
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case(3)
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Cx = Fx2*Fx1
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case default
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Cx = 1.d0
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end select
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! Compute GIC-GGA exchange energy
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Ex = 0d0
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do iG=1,nGrid
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r = max(0d0,rho(iG))
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if(r > threshold) then
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g = drho(1,iG)**2 + drho(2,iG)**2 + drho(3,iG)**2
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x = sqrt(g)/r**(4d0/3d0)
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Ex = Ex + weight(iG)*r**(4d0/3d0)*(CxLSDA - b*x**2/(1d0 + 6d0*b*x*asinh(x)))
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end if
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end do
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Ex = Cx*Ex
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end subroutine CC_B88_gga_exchange_energy
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