./41_xc_lowlevel/xclb.F90

ABINIT/xclb

ABINIT/xclb [ Functions ]

NAME

 xclb

FUNCTION

 Computes the GGA like part (vx_lb) of the Leeuwen-Baerends
 exchange-correlation potential (vxc_lb) and adds it to the
 lda exchange-correlation potential (vxc_lda) which
 must be provided as input,
            vxci  <--  vxc_lb =: vxc_lda + vx_lb

 [R van Leeuwen and EJ Baerends, Phys Rev A 49, 2421 (1994)]

 With respect to spin, the van Leeuwen-Baerends
 potential is "exchange-like" : separate contributions from
 spin up and spin down.

 Copyright (C) 2000-2018 ABINIT group (MF,LG)
 This file is distributed under the terms of the
 GNU General Public License, see ~abinit/COPYING
 or http://www.gnu.org/copyleft/gpl.txt .
 For the initials of contributors, see ~abinit/doc/developers/contributors.txt .

INPUTS

  npts= number of points to be computed
  nspden=1 for unpolarized, 2 for spin-polarized
  grho2_updn(npts,2*nspden-1)=square of the gradient of the spin-up,
     and, if nspden==2, spin-down, and total density (Hartree/Bohr**2)
  rho_updn(npts,nspden)=spin-up and spin-down density (Hartree/bohr**3)

OUTPUT

  (see side effects)

SIDE EFFECTS

 Input/Output:
  vxci(npts,nspden)=input xc potential to which Leeuwen-Baerends correction
   is added at output.

PARENTS

      drivexc

CHILDREN

SOURCE

 48 #if defined HAVE_CONFIG_H
 49 #include "config.h"
 50 #endif
 51 
 52 #include "abi_common.h"
 53 
 54 
 55 subroutine xclb(grho2_updn,npts,nspden,rho_updn,vxci)
 56 
 57  use defs_basis
 58  use m_profiling_abi
 59 
 60 !This section has been created automatically by the script Abilint (TD).
 61 !Do not modify the following lines by hand.
 62 #undef ABI_FUNC
 63 #define ABI_FUNC 'xclb'
 64 !End of the abilint section
 65 
 66  implicit none
 67 
 68 !Arguments ------------------------------------
 69 !scalars
 70  integer,intent(in) :: npts,nspden
 71 !arrays
 72  real(dp),intent(in) :: grho2_updn(npts,2*nspden-1),rho_updn(npts,nspden)
 73  real(dp),intent(inout) :: vxci(npts,nspden)
 74 
 75 !Local variables-------------------------------
 76 !scalars
 77  integer :: ipts,ispden
 78  real(dp),parameter :: beta=0.05_dp
 79  real(dp) :: density,density_gradient,density_t13,s_g_sq,scaled_gradient
 80  real(dp) :: scaling_factor,vx_lb
 81 
 82 ! *************************************************************************
 83 
 84 !DEBUG
 85 !write(std_out,*) ' %xclb: enter'
 86 !ENDDEBUG
 87 
 88 !scale the spin densities for evaluating spin up or down exchange
 89  scaling_factor=one
 90  if(nspden == 2) scaling_factor=two
 91 
 92  do ispden=1,nspden
 93 
 94    do ipts=1,npts
 95 
 96      density= scaling_factor * rho_updn(ipts,ispden)
 97      density_gradient= scaling_factor * sqrt(grho2_updn(ipts,ispden))
 98 
 99      density_t13= density**third
100      scaled_gradient= density_gradient/max(density*density_t13,1.e-12_dp)
101 
102      s_g_sq= scaled_gradient*scaled_gradient
103 
104      vx_lb= -beta*density_t13 * s_g_sq/ &
105 &     (one+3.d0*beta* scaled_gradient*log(scaled_gradient+sqrt(one+s_g_sq*s_g_sq)))
106 
107      vxci(ipts,ispden)=vxci(ipts,ispden)+vx_lb
108    end do
109 
110  end do
111 
112 end subroutine xclb

TABLE OF CONTENTS

ABINIT/xclb [ Functions ]