[Pw_forum] Fixing magnetization in a given direction for "vc-relax" or relax calculations

[mohnish pandey]

Dear QE users,

I am trying to optimize the structure of MnSe which in ground state has
magnetization in (111) direction. I am considering three type of unit cells
for the calculation (1) The cubic unit cell(8 atoms) (2) Rhobohedral(4
atoms) (3) Hexagonal(12 atoms). But as in cubic unit cell and rhombohedral
unit cell the default value of the magnetization direction is along the
z-axis which is not same as (111) whereas in hexagonal unit cell with
magnetization along z-axis is same as (111). My question is can we fix the
magnetization direction for example in rhombohedral unit cell along (111)
for "vc-relax" or "relax" calculation? I tried the non-collinear option
with giving the direction but after a scf cycle it shows that "stress not
implemented in non-collinear option" for vc-relax calculation. And when I
do the calculation for cubic and rhombohedral unit cell the individual
magnetization that I am getting is around ~0.4 (which is very small) and
for the hexagonal unit cell its about ~4. So there is lot of difference I
am getting in changing the type of unit cell. Somebody please give a
suggestion for overcoming the problem. Thanks a lot in advance.

-- 
Regards,
MOHNISH,
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Mohnish Pandey
BTech-Mtech, IIT Kanpur
Senior Project Associate,
Department of Chemical Engineering,
IIT KANPUR, UP, INDIA
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