From a8cbb5668bdd1914ec6764eb956da05f90bfd362 Mon Sep 17 00:00:00 2001
From: Nicolas Essing <n.essing@fz-juelich.de>
Date: Thu, 4 Nov 2021 15:49:07 +0100
Subject: [PATCH] Fix torque based constraints for negative moments.
The constraint magnetic field that is calculated based on the torque
is now muliplied by the sign of the magnetic moment in the local
frame of reference.
The torque has to be understood as an energy related to a change in
the direction of the local frame of reference. This can differ from
the direction of the magnetic moment by a sign. For the constraint
fields, the energy related to a change of the direction of the moment
is needed, so this sign has to be put at this point.
(This is probably somewhat confusing, I'll add a better explanation
and probably some sketch to the documentation of these features.)
---
source/KKRnano/source/bfield/torque.f90 | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/source/KKRnano/source/bfield/torque.f90 b/source/KKRnano/source/bfield/torque.f90
index d61174350..a061c7ca9 100644
--- a/source/KKRnano/source/bfield/torque.f90
+++ b/source/KKRnano/source/bfield/torque.f90
@@ -164,7 +164,7 @@ contains
double precision, dimension(3) :: dir, mag_mom_dir
double precision, dimension(3) :: old_b_constr
- double precision :: mag_mom_len
+ double precision :: mag_mom_len, mag_mom_sign
! If the current iteration is not in the window the magnetic fields should be
! applied, return without changing the potential
@@ -177,13 +177,16 @@ contains
dir(2) = sin(theta) * sin(phi)
dir(3) = cos(theta)
- ! Calculate direction and absolute value of the magnetic moment
+ ! Calculate direction and absolute value of the magnetic moment and the
+ ! sign the magnetic moment has in the local frame of reference
mag_mom_len = sqrt(dot_product(bfield%mag_mom(:), bfield%mag_mom(:)))
mag_mom_dir = bfield%mag_mom(:) / mag_mom_len
+ mag_mom_sign = sign(1., dot_product(mag_mom_dir, dir))
if (constr_mode == 3) then
bfield%bfield_constr(:) = bfield%bfield_constr(:) - &
- (bfield%mag_torque(:) / mag_mom_len) * constr_bfield_mixing
+ ( mag_mom_sign * (bfield%mag_torque(:) / mag_mom_len) * &
+ constr_bfield_mixing )
else if (constr_mode == 2) then
old_b_constr = bfield%bfield_constr(:)
bfield%bfield_constr(:) = old_b_constr - dot_product(old_b_constr,dir)*dir - &
--
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