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! Copyright (C) 2002-2005 J. K. Dewhurst, S. Sharma and C. Ambrosch-Draxl.
! This file is distributed under the terms of the GNU General Public License.
! See the file COPYING for license details.
!BOP
! !ROUTINE: bfieldfsm
! !INTERFACE:
subroutine bfieldfsm
! !USES:
use modmain
! !DESCRIPTION:
! Updates the effective magnetic field, ${\bf B}_{\rm FSM}$, required for
! fixing the spin moment to a given value, ${\bf M}_{\rm FSM}$. This is done
! by adding a vector to the field which is proportional to the difference
! between the moment calculated in the $i$th self-consistent loop and the
! required moment:
! $$ {\bf B}_{\rm FSM}^{i+1}={\bf B}_{\rm FSM}^i+\lambda\left({\bf M}^i
! -{\bf M}_{\rm FSM}\right), $$
! where $\lambda$ is a scaling factor.
!
! !REVISION HISTORY:
! Created March 2005 (JKD)
!EOP
!BOC
implicit none
! local variables
integer is,ia,ias
real(8) v1(3),v2(3),t1,t2
if ((.not.spinpol).or.(fsmtype == 0)) return
! fixed spin direction not valid for collinear magnetism
if ((.not.ncmag).and.(fsmtype < 0)) return
! determine the global effective field
if ((abs(fsmtype) == 1).or.(abs(fsmtype) == 3)) then
if (ncmag) then
v1(:)=momtot(:)
else
v1(:)=0.d0
v1(3)=momtot(1)
end if
v2(:)=v1(:)-momfix(:)
if (ncmag) then
bfsmc(:)=bfsmc(:)+taufsm*v2(:)
else
bfsmc(1)=bfsmc(1)+taufsm*v2(3)
end if
! make sure that the constraining field is perpendicular to the fixed moment
! for fixed direction calculations (Y. Kvashnin and LN)
if (fsmtype < 0) call r3vo(momfix,bfsmc)
end if
! determine the muffin-tin fields for fixed local moments
if ((abs(fsmtype) == 2).or.(abs(fsmtype) == 3)) then
do is=1,nspecies
do ia=1,natoms(is)
ias=idxas(ia,is)
! if any component is >= 1000 then do not fix the moment
if (any(abs(mommtfix(1:3,ia,is)) >= 1000.d0)) cycle
if (ncmag) then
v1(:)=mommt(:,ias)
else
v1(:)=0.d0
v1(3)=mommt(1,ias)
end if
v2(:)=v1(:)-mommtfix(:,ia,is)
if (ncmag) then
bfsmcmt(:,ias)=bfsmcmt(:,ias)+taufsm*v2(:)
else
bfsmcmt(1,ias)=bfsmcmt(1,ias)+taufsm*v2(3)
end if
! fixed spin direction
if (fsmtype < 0) call r3vo(mommtfix(:,ia,is),bfsmcmt(:,ias))
end do
end do
end if
! global fixed spin magnitude
if ((fsmtype == 4).or.(fsmtype == 6)) then
t1=taufsm*(momtotm-momfixm)
bfsmc(1:ndmag)=bfsmc(1:ndmag)+t1*momtot(1:ndmag)
end if
! local fixed spin magnitude
if ((fsmtype == 5).or.(fsmtype == 6)) then
do is=1,nspecies
do ia=1,natoms(is)
ias=idxas(ia,is)
t1=mommtfixm(ia,is)
if (t1 < 0.d0) cycle
t2=norm2(mommt(1:ndmag,ias))
t1=taufsm*(t2-t1)
bfsmcmt(1:ndmag,ias)=bfsmcmt(1:ndmag,ias)+t1*mommt(1:ndmag,ias)
end do
end do
end if
end subroutine
!EOC
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