mirror of https://gitlab.com/QEF/q-e.git
182 lines
5.5 KiB
Fortran
182 lines
5.5 KiB
Fortran
!
|
|
! Copyright (C) 2001 PWSCF group
|
|
! This file is distributed under the terms of the
|
|
! GNU General Public License. See the file `License'
|
|
! in the root directory of the present distribution,
|
|
! or http://www.gnu.org/copyleft/gpl.txt .
|
|
!
|
|
#include "f_defs.h"
|
|
!
|
|
!-----------------------------------------------------------------------
|
|
subroutine do_shift_ew (alat, nat, ntyp, ityp, zv, delta_zv, at, bg, tau, &
|
|
omega, g, gg, ngm, gcutm, gstart, gamma_only, shift_ion)
|
|
!-----------------------------------------------------------------------
|
|
!
|
|
! Calculates Ewald energy with both G- and R-space terms.
|
|
! Determines optimal alpha. Should hopefully work for any structure.
|
|
!
|
|
!
|
|
USE kinds
|
|
implicit none
|
|
!
|
|
! first the dummy variables
|
|
!
|
|
|
|
integer :: nat, ntyp, ityp (nat), ngm, gstart
|
|
! input: number of atoms in the unit cell
|
|
! input: number of different types of atoms
|
|
! input: the type of each atom
|
|
! input: number of plane waves for G sum
|
|
! input: first non-zero G vector
|
|
|
|
logical :: gamma_only
|
|
|
|
real(DP) :: tau (3, nat), g (3, ngm), gg (ngm), zv (ntyp), &
|
|
at (3, 3), bg (3, 3), omega, alat, gcutm, delta_zv(ntyp), &
|
|
shift_ion(nat)
|
|
! input: the positions of the atoms in the cell
|
|
! input: the coordinates of G vectors
|
|
! input: the square moduli of G vectors
|
|
! input: the charge of each type of atoms
|
|
! input: the direct lattice vectors
|
|
! input: the reciprocal lattice vectors
|
|
! input: the volume of the unit cell
|
|
! input: lattice parameter
|
|
! input: cut-off of g vectors
|
|
real(DP) :: ewald
|
|
! output: the ewald energy
|
|
!
|
|
! here the local variables
|
|
!
|
|
integer, parameter :: mxr = 50
|
|
! the maximum number of R vectors included in r
|
|
real(DP), parameter :: tpi = 2.d0 * 3.141592653589793d0
|
|
real(DP), parameter :: e2 = 2.d0
|
|
! the square of the electron charge (Ry atomic units)
|
|
integer :: ng, nr, na, nb, nt, nrm, ipol
|
|
! counter over reciprocal G vectors
|
|
! counter over direct vectors
|
|
! counter on atoms
|
|
! counter on atoms
|
|
! counter on atomic types
|
|
! number of R vectors included in r sum
|
|
! counter on polarization
|
|
|
|
real(DP) :: charge, tpiba2, ewaldg, ewaldr, dtau (3), alpha, &
|
|
r (3, mxr), r2 (mxr), rmax, rr, upperbound, fact, arg
|
|
! total ionic charge in the cell
|
|
! length in reciprocal space
|
|
! ewald energy computed in reciprocal space
|
|
! ewald energy computed in real space
|
|
! the difference tau_s - tau_s'
|
|
! alpha term in ewald sum
|
|
! input of the rgen routine ( not used here )
|
|
! the square modulus of R_j-tau_s-tau_s'
|
|
! the maximum radius to consider real space sum
|
|
! buffer variable
|
|
! used to optimize alpha
|
|
complex(DP), allocatable :: rhon(:)
|
|
real(DP), external :: erfc
|
|
|
|
allocate (rhon(ngm))
|
|
|
|
shift_ion(:) = 0.d0
|
|
|
|
tpiba2 = (tpi / alat) **2
|
|
charge = 0.d0
|
|
do na = 1, nat
|
|
charge = charge+zv (ityp (na) )
|
|
enddo
|
|
alpha = 2.9d0
|
|
100 alpha = alpha - 0.1d0
|
|
!
|
|
! choose alpha in order to have convergence in the sum over G
|
|
! upperbound is a safe upper bound for the error in the sum over G
|
|
!
|
|
if (alpha.le.0.d0) call errore ('ewald', 'optimal alpha not found', 1)
|
|
upperbound = 2.d0 * charge**2 * sqrt (2.d0 * alpha / tpi) * erfc ( &
|
|
sqrt (tpiba2 * gcutm / 4.d0 / alpha) )
|
|
if (upperbound.gt.1.0d-7) goto 100
|
|
!
|
|
! G-space sum here.
|
|
! Determine if this processor contains G=0 and set the constant term
|
|
!
|
|
if (gstart==2) then
|
|
do na =1,nat
|
|
shift_ion(na) = - charge * delta_zv(ityp(na)) /alpha/ 4.0
|
|
end do
|
|
endif
|
|
if (gamma_only) then
|
|
fact = 2.d0
|
|
else
|
|
fact = 1.d0
|
|
end if
|
|
do ng = gstart, ngm
|
|
rhon(ng) = (0.d0, 0.d0)
|
|
do na =1, nat
|
|
arg = (g (1, ng) * tau (1, na) + &
|
|
g (2, ng) * tau (2, na) + &
|
|
g (3, ng) * tau (3, na) ) * tpi
|
|
rhon(ng) = rhon(ng) + zv (ityp(na)) * CMPLX (cos (arg), -sin (arg))
|
|
enddo
|
|
end do
|
|
do na=1,nat
|
|
do ng=gstart, ngm
|
|
arg = (g (1, ng) * tau (1, na) + g (2, ng) * tau (2, na) &
|
|
+ g (3, ng) * tau (3, na) ) * tpi
|
|
shift_ion(na) = shift_ion(na) + fact * delta_zv(ityp(na)) * &
|
|
CONJG(rhon(ng)) * CMPLX (cos (arg), -sin (arg)) * &
|
|
exp ( -gg(ng)*tpiba2/alpha/4.d0) / gg(ng)/tpiba2
|
|
enddo
|
|
enddo
|
|
shift_ion(:) = 2.d0 * tpi / omega * shift_ion(:)
|
|
!
|
|
! Here add the other constant term
|
|
!
|
|
if (gstart.eq.2) then
|
|
do na = 1, nat
|
|
shift_ion(na) = shift_ion(na) - &
|
|
zv (ityp (na) ) * delta_zv(ityp(na)) * &
|
|
sqrt (8.d0/tpi*alpha)
|
|
enddo
|
|
endif
|
|
!
|
|
! R-space sum here (only for the processor that contains G=0)
|
|
!
|
|
if (gstart.eq.2) then
|
|
rmax = 4.d0 / sqrt (alpha) / alat
|
|
!
|
|
! with this choice terms up to ZiZj*erfc(4) are counted (erfc(4)=2x10^-8
|
|
!
|
|
do na = 1, nat
|
|
do nb = 1, nat
|
|
do ipol = 1, 3
|
|
dtau (ipol) = tau (ipol, na) - tau (ipol, nb)
|
|
enddo
|
|
!
|
|
! generates nearest-neighbors shells
|
|
!
|
|
call rgen (dtau, rmax, mxr, at, bg, r, r2, nrm)
|
|
!
|
|
! and sum to the real space part
|
|
!
|
|
do nr = 1, nrm
|
|
rr = sqrt (r2 (nr) ) * alat
|
|
shift_ion(na) = shift_ion(na) + &
|
|
delta_zv(ityp(na)) * zv (ityp (nb) ) * &
|
|
erfc ( sqrt (alpha) * rr) / rr
|
|
enddo
|
|
enddo
|
|
enddo
|
|
endif
|
|
|
|
shift_ion(:) = e2 * shift_ion(:)
|
|
|
|
#ifdef __PARA
|
|
call reduce (nat, shift_ion)
|
|
#endif
|
|
deallocate (rhon)
|
|
return
|
|
end subroutine do_shift_ew
|
|
|