How to change the value of spin

[Jian Yao]

Dear vampire developers and users,

I want to know how to set the value of spin, for instance, if I want to simulate dynamics of spin with spin = 5/2 , instead of the default value 1, how can I set it? Thanks a lot!

Best,

Jian

[Gavin Abo]

Have a look at the VAMPIRE 6.0 manual [1].  On page 65 and 68, it might be the atomic-spin-moment and initial-spin-direction that you are looking for:

material:atomic-spin-moment = float [0.01+ μB, default 1.72 μB ] Defines
the local effective spin moment for each atomic site.

material:initial-spin-direction float vector /bool [default (001) / false] Deter-
mines the initial direction of the spins in the material.

In an Ising model [2], it looks like σ could be set to +5/2 or -5/2.

In the Monte Carlo model that VAMPIRE uses [3], it looks like you could set the initial + or - direction of S in the Hamiltonian with the initial-spin-direction.

It looks like the default is:

material[1]:initial-spin-direction=0,0,1

Depending on what you need, it look like you could set it in the +z direction

material[1]:initial-spin-direction=0,0,1

the -z direction

material[1]:initial-spin-direction=0,0,-1

the x direction

material[1]:initial-spin-direction=1,0,0

or y direction

material[1]:initial-spin-direction=0,1,0

What I'm not sure about is the magnitude of S.  I'm thinking that might be related to equation 30 in [3] or the atomic spin moment.

[1] https://vampire.york.ac.uk/resources/vampire-manual.pdf
[2] https://en.wikipedia.org/wiki/Ising_model
[3] https://doi.org/10.1088/0953-8984/26/10/103202

Hopefully that can help and kind regards,

Gavin
VAMPIRE user