2020-04-06 22:27:13 +02:00
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subroutine RB88_gga_exchange_individual_energy(nGrid,weight,rhow,drhow,rho,drho,Ex)
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! Compute restricted Becke's GGA indivudal energy
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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) :: nGrid
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double precision,intent(in) :: weight(nGrid)
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double precision,intent(in) :: rhow(nGrid)
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double precision,intent(in) :: drhow(ncart,nGrid)
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double precision,intent(in) :: rho(nGrid)
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double precision,intent(in) :: drho(ncart,nGrid)
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! Local variables
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integer :: iG
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double precision :: alpha
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double precision :: beta
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double precision :: r,rI,g,x
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double precision :: ex_p,dexdr_p
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! Output variables
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double precision,intent(out) :: Ex
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! Coefficients for B88 GGA exchange functional
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alpha = -(3d0/2d0)*(3d0/(4d0*pi))**(1d0/3d0)
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beta = 0.0042d0
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! Compute GGA exchange matrix in the AO basis
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Ex = 0d0
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do iG=1,nGrid
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r = max(0d0,0.5d0*rhow(iG))
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rI = max(0d0,0.5d0*rho(iG))
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2020-07-06 15:42:21 +02:00
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if(r > threshold .or. rI > threshold) then
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2020-04-06 22:27:13 +02:00
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g = 0.25d0*(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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dexdr_p = 4d0/3d0*r**(1d0/3d0)*(alpha - beta*g**(3d0/4d0)/r**2) &
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+ 2d0*beta*g**(3d0/4d0)/r**(5d0/3d0) &
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- 2d0*3d0/4d0*beta*g**(-1d0/4d0)/r**(2d0/3d0)
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ex_p = alpha*r**(4d0/3d0) &
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- weight(iG)*beta*x**2*r**(4d0/3d0)/(1d0 + 6d0*beta*x*asinh(x))
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Ex = Ex + weight(iG)*(ex_p*rI + dexdr_p*r*rI - dexdr_p*r*r)
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end if
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end do
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end subroutine RB88_gga_exchange_individual_energy
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