From ad5c240dc69b68f6c932722b0cd71d6d012d93f2 Mon Sep 17 00:00:00 2001
From: Nicolas Essing <n.essing@fz-juelich.de>
Date: Sun, 28 Nov 2021 14:44:35 +0100
Subject: [PATCH] Changed definition of torque (by a factor of the magnetic
moment size).
The magnetic torque can be defined either as the derivative of the
total energy with respect to the magnetic moment direction
(T = dE/de) or as the perpendicular part of the derivative of the
total energy with respect to the magnetic moment (T = P dE/dm).
As de = 1/|m| P dm, the two definitions have the same directions
and differ by the factor 1/|m|.
So far, the first definition was used.
However, we decided to switch to the second, as it is easier comparable
to the constraint magnetic field (same units) and thus also makes it
easier to use the torque in scripts or as an initial guess for constraint
magnetic fields.
!! Note that his commit might BREAK COMPATIBILITY with previus scripts !!
---
source/KKRnano/source/bfield/torque.f90 | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/source/KKRnano/source/bfield/torque.f90 b/source/KKRnano/source/bfield/torque.f90
index 51d3638f9..48b4af1fd 100644
--- a/source/KKRnano/source/bfield/torque.f90
+++ b/source/KKRnano/source/bfield/torque.f90
@@ -49,6 +49,8 @@ contains
integer :: irmd, lmmax, lmpotd ! radial and angular momentum sizes
integer :: i, ir, ilm ! generic, radial and angular momentum loop indices
double complex :: integrate_result ! to output the result of some integrations
+ double precision :: mag_mom_len ! absolute value of magnetic moment
+ double precision :: mag_mom_len_mt ! absolute value of magnetic moment over muffin tin
double precision, dimension(3) :: dir ! unit vectors of old magnetic moment
double precision, dimension(3) :: torque, torque_mt ! torque calculated over whole cell or mt only
double complex, dimension(2,2) :: rho2ns_temp ! temporary matrix to rotate rho2nsc
@@ -111,7 +113,10 @@ contains
mag_mt(ilm,i) = real(integrate_result * rfpi)
end do
end do
-
+
+ mag_mom_len = sqrt(dot_product(mag(1,:), mag(1,:)))
+ mag_mom_len_mt = sqrt(dot_product(mag_mt(1,:), mag_mt(1,:)))
+
! Calculate the torque (also mt and end)
! Integrate the xc bfield times the magnetization density.
torque(:) = 0.
@@ -127,7 +132,11 @@ contains
torque_mt(i) = torque_mt(i) + real(integrate_result * rfpi)
end do
end do
-
+
+ ! Divide by magnetic moment
+ torque(:) = torque(:) / mag_mom_len
+ torque_mt(:) = torque_mt(:) / mag_mom_len_mt
+
! Project torque to perpendicular of magnetic moment
dir(1) = sin(theta) * cos(phi)
dir(2) = sin(theta) * sin(phi)
@@ -188,8 +197,7 @@ contains
if (constr_mode == 3) then
bfield%bfield_constr(:) = bfield%bfield_constr(:) - &
- ( mag_mom_sign * (bfield%mag_torque(:) / mag_mom_len) * &
- constr_bfield_mixing )
+ ( mag_mom_sign * bfield%mag_torque(:) * 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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