2020-10-14 23:31:14 +02:00
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subroutine US51_lda_exchange_energy(nGrid,weight,rho,Ex)
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2019-03-13 11:07:31 +01:00
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2020-10-14 15:07:35 +02:00
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use xc_f90_lib_m
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2019-03-13 11:07:31 +01:00
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! Compute Slater's LDA exchange 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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2020-10-14 23:31:14 +02:00
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double precision :: alpha,r,alphaw,a2,b2,c2,a1,b1,c1
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2019-03-13 11:07:31 +01:00
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2020-10-14 16:02:09 +02:00
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! Output variables
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2020-07-02 14:27:38 +02:00
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2020-10-14 23:31:14 +02:00
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double precision :: Ex
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! Cx coefficient for Slater LDA exchange
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2019-03-13 11:07:31 +01:00
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2020-10-14 23:31:14 +02:00
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alpha = -(3d0/2d0)*(3d0/(4d0*pi))**(1d0/3d0)
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2019-03-13 11:07:31 +01:00
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2020-10-14 23:31:14 +02:00
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! Compute LDA exchange energy
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2019-03-13 11:07:31 +01:00
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2020-10-14 23:31:14 +02:00
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Ex = 0d0
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do iG=1,nGrid
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2019-03-13 11:07:31 +01:00
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2020-10-14 23:31:14 +02:00
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r = max(0d0,rho(iG))
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2019-03-13 11:07:31 +01:00
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2020-10-14 23:31:14 +02:00
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if(r > threshold) then
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2019-03-13 11:07:31 +01:00
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2020-10-14 23:31:14 +02:00
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Ex = Ex + weight(iG)*alpha*r**(4d0/3d0)
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2019-03-13 11:07:31 +01:00
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2020-10-14 23:31:14 +02:00
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endif
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2019-03-13 11:07:31 +01:00
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2020-10-14 23:31:14 +02:00
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enddo
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2019-03-13 11:07:31 +01:00
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2020-07-02 14:27:38 +02:00
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end subroutine US51_lda_exchange_energy
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