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https://github.com/pfloos/quack
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138 lines
3.5 KiB
Fortran
138 lines
3.5 KiB
Fortran
subroutine VWN5_lda_correlation_energy(nGrid,weight,rho,Ec)
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! Compute 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,nspin)
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! Local variables
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integer :: iG
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double precision :: ra,rb,r,rs,x,z
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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 :: a_f,x0_f,xx0_f,b_f,c_f,x_f,q_f
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double precision :: a_a,x0_a,xx0_a,b_a,c_a,x_a,q_a
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double precision :: ec_z,ec_p,ec_f,ec_a
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double precision :: fz,d2fz
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! Output variables
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double precision :: Ec(nsp)
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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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a_f = +0.0621814D0/4D0
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x0_f = -0.325d0
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b_f = +7.06042d0
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c_f = +18.0578d0
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a_a = -1d0/(6d0*pi**2)
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x0_a = -0.0047584D0
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b_a = 1.13107d0
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c_a = 13.0045d0
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! Initialization
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Ec(:) = 0d0
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do iG=1,nGrid
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ra = max(0d0,rho(iG,1))
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rb = max(0d0,rho(iG,2))
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! alpha-alpha contribution
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if(ra > threshold) then
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rs = (4d0*pi*ra/3d0)**(-1d0/3d0)
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x = sqrt(rs)
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x_f = x*x + b_f*x + c_f
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xx0_f = x0_f*x0_f + b_f*x0_f + c_f
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q_f = sqrt(4d0*c_f - b_f*b_f)
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ec_f = a_f*( log(x**2/x_f) + 2d0*b_f/q_f*atan(q_f/(2d0*x + b_f)) &
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- b_f*x0_f/xx0_f*( log((x - x0_f)**2/x_f) + 2d0*(b_f + 2d0*x0_f)/q_f*atan(q_f/(2d0*x + b_f)) ) )
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Ec(1) = Ec(1) + weight(iG)*ec_f*ra
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end if
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! alpha-beta contribution
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if(ra > threshold .and. rb > threshold) then
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r = ra + rb
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rs = (4d0*pi*r/3d0)**(-1d0/3d0)
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z = (ra - rb)/r
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x = sqrt(rs)
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fz = (1d0 + z)**(4d0/3d0) + (1d0 - z)**(4d0/3d0) - 2d0
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fz = fz/(2d0*(2d0**(1d0/3d0) - 1d0))
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d2fz = 4d0/(9d0*(2**(1d0/3d0) - 1d0))
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x_p = x*x + b_p*x + c_p
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x_f = x*x + b_f*x + c_f
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x_a = x*x + b_a*x + c_a
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xx0_p = x0_p*x0_p + b_p*x0_p + c_p
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xx0_f = x0_f*x0_f + b_f*x0_f + c_f
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xx0_a = x0_a*x0_a + b_a*x0_a + c_a
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q_p = sqrt(4d0*c_p - b_p*b_p)
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q_f = sqrt(4d0*c_f - b_f*b_f)
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q_a = sqrt(4d0*c_a - b_a*b_a)
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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_f = a_f*( log(x**2/x_f) + 2d0*b_f/q_f*atan(q_f/(2d0*x + b_f)) &
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- b_f*x0_f/xx0_f*( log((x - x0_f)**2/x_f) + 2d0*(b_f + 2d0*x0_f)/q_f*atan(q_f/(2d0*x + b_f)) ) )
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ec_a = a_a*( log(x**2/x_a) + 2d0*b_a/q_a*atan(q_a/(2d0*x + b_a)) &
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- b_a*x0_a/xx0_a*( log((x - x0_a)**2/x_a) + 2d0*(b_a + 2d0*x0_a)/q_a*atan(q_a/(2d0*x + b_a)) ) )
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ec_z = ec_p + ec_a*fz/d2fz*(1d0-z**4) + (ec_f - ec_p)*fz*z**4
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Ec(2) = Ec(2) + weight(iG)*ec_z*r
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end if
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! beta-beta contribution
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if(rb > threshold) then
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rs = (4d0*pi*rb/3d0)**(-1d0/3d0)
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x = sqrt(rs)
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x_f = x*x + b_f*x + c_f
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xx0_f = x0_f*x0_f + b_f*x0_f + c_f
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q_f = sqrt(4d0*c_f - b_f*b_f)
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ec_f = a_f*( log(x**2/x_f) + 2d0*b_f/q_f*atan(q_f/(2d0*x + b_f)) &
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- b_f*x0_f/xx0_f*( log((x - x0_f)**2/x_f) + 2d0*(b_f + 2d0*x0_f)/q_f*atan(q_f/(2d0*x + b_f)) ) )
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Ec(3) = Ec(3) + weight(iG)*ec_f*rb
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end if
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end do
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Ec(2) = Ec(2) - Ec(1) - Ec(3)
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end subroutine VWN5_lda_correlation_energy
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