! Copyright (C) 2002-2005 J. K. Dewhurst, S. Sharma and C. Ambrosch-Draxl. ! This file is distributed under the terms of the GNU Lesser General Public ! License. See the file COPYING for license details. !BOP ! !ROUTINE: xc_pzca ! !INTERFACE: subroutine xc_pzca(n,rho,ex,ec,vx,vc) ! !INPUT/OUTPUT PARAMETERS: ! n : number of density points (in,integer) ! rho : charge density (in,real(n)) ! ex : exchange energy density (out,real(n)) ! ec : correlation energy density (out,real(n)) ! vx : exchange potential (out,real(n)) ! vc : correlation potential (out,real(n)) ! !DESCRIPTION: ! Spin-unpolarised exchange-correlation potential and energy of the ! Perdew-Zunger parameterisation of Ceperley-Alder electron gas: {\it Phys. ! Rev. B} {\bf 23}, 5048 (1981) and {\it Phys. Rev. Lett.} {\bf 45}, 566 ! (1980). ! ! !REVISION HISTORY: ! Created October 2002 (JKD) !EOP !BOC implicit none ! arguments integer, intent(in) :: n real(8), intent(in) :: rho(n) real(8), intent(out) :: ex(n),ec(n),vx(n),vc(n) ! local variables integer i real(8), parameter :: pi=3.1415926535897932385d0 real(8), parameter :: thrd=1.d0/3.d0, thrd2=2.d0/3.d0, thrd4=4.d0/3.d0 real(8), parameter :: g=-0.1423d0,b1=1.0529d0,b2=0.3334d0 real(8), parameter :: a=0.0311d0,b=-0.048d0,c=0.0020d0,d=-0.0116d0 real(8) p1,p2,r,rs,t1 if (n.le.0) then write(*,*) write(*,'("Error(xc_pzca): invalid n : ",I8)') n write(*,*) stop end if ! prefactors t1=3.d0/(4.d0*pi) p1=t1**thrd p2=t1*(9.d0*pi/4.d0)**thrd do i=1,n r=rho(i) if (r.lt.1.d-12) then ex(i)=0.d0 ec(i)=0.d0 vx(i)=0.d0 vc(i)=0.d0 cycle end if rs=p1/r**thrd ! exchange energy and potential ex(i)=-p2/rs vx(i)=thrd4*ex(i) ! correlation energy and potential if (rs.ge.1.d0) then t1=sqrt(rs) ec(i)=g/(1.d0+b1*t1+b2*rs) vc(i)=ec(i)*(1.d0+(7.d0/6.d0)*b1*t1+thrd4*b2*rs)/(1.d0+b1*t1+b2*rs) else t1=dlog(rs) ec(i)=a*t1+b+c*rs*t1+d*rs vc(i)=a*t1+(b-thrd*a)+thrd2*c*rs*t1+thrd*(2.d0*d-c)*rs end if end do return end subroutine !EOC