Tc calculation of exchange energy

[Muzaffer Baloch]

Hi Vampire Users,

I want to calculate Tc for the Sample of MnCuCoFe204, i am confused regarding the calculation of exchange matrix value.? I dont have experimental Tc value. How to calculate exchange matrix and is it necessary to be in mat.file.?

Thanks in Advance

Muzaffar Ali

[Gavin Abo]

Unfortunately, I'm not currently familiar with the structure of MnCuCoFe204.

That shouldn't be a concern as long as the structure can be defined in
one of the built-in or orthogonal structures at the following two links:

[1]
https://vampire.york.ac.uk/tutorials/system-generation/crystal-structure/
[2] https://vampire.york.ac.uk/tutorials/system-generation/complex-crystals/

However, if it is not one of those structures than it could be difficult
or not possible for someone to currently do unless they are experienced
such as with programming and crystallography.

If the structure happens to be a non-orthogonal, those cells are not yet
supported as explained at the following link:

[3] https://groups.google.com/g/vampire-users/c/ubgiSq3X9AY/m/PgNtvEnECQAJ

Whether the exchange matrix is needed in the mat file should depend on
the type of exchange that you need for you simulation model.

If for the exchange you need the exchange-matrix, which is described in
the manual [4], than that goes in the mat file and not the ucf [5].

There are other exchange types mentioned at [6] that need to instead be
defined in the ucf.

To calculate the exchange values, equation (9) in [7] can be used if it
is one of the structures were the coordination number z and correction
factor ε are known (i.e., see [1]).  Or you are not able find the values
in literature then may need to calculate them with another method such
as with a Density Functional Theory (DFT) program like TB2J (for some
for information on that, refer to [8]).

[4] https://vampire.york.ac.uk/resources/vampire-manual.pdf
[5] https://groups.google.com/g/vampire-users/c/t_8kPSA3g3U/m/0dZ5nr7WBAAJ
[6] https://groups.google.com/g/vampire-users/c/tZLKjnZbjFY/m/MIv0gbMIBAAJ
[7] https://doi.org/10.1088/0953-8984/26/10/103202
[8] https://groups.google.com/g/vampire-users/c/5-FANO0dHqo/m/eVB94SWuBAAJ

Kind Regards,

Gavin
VAMPIRE user