2020-03-15 20:33:18 +01:00
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subroutine RVWN5_lda_correlation_energy(nGrid,weight,rho,Ec)
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! Compute the restricted VWN5 LDA correlation 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) :: rho(nGrid)
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! Local variables
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integer :: iG
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double precision :: r,rs,x
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double precision :: a_p,x0_p,xx0_p,b_p,c_p,x_p,q_p
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double precision :: ec_p
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! Output variables
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2020-03-17 19:35:00 +01:00
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double precision :: Ec
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2020-03-15 20:33:18 +01:00
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! Parameters of the functional
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a_p = +0.0621814D0/2D0
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x0_p = -0.10498d0
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b_p = +3.72744d0
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c_p = +12.9352d0
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! Initialization
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Ec = 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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rs = (4d0*pi*r/3d0)**(-1d0/3d0)
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x = sqrt(rs)
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x_p = x*x + b_p*x + c_p
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xx0_p = x0_p*x0_p + b_p*x0_p + c_p
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q_p = sqrt(4d0*c_p - b_p*b_p)
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ec_p = a_p*( log(x**2/x_p) + 2d0*b_p/q_p*atan(q_p/(2d0*x + b_p)) &
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- b_p*x0_p/xx0_p*( log((x - x0_p)**2/x_p) + 2d0*(b_p + 2d0*x0_p)/q_p*atan(q_p/(2d0*x + b_p)) ) )
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Ec = Ec + weight(iG)*ec_p*r
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end if
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end do
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end subroutine RVWN5_lda_correlation_energy
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