NCM calculations

Dear ELK users,

using NCM, how to find automatically (auto-optimization by ELK) the spins orientations which correspond to the ground state, or we have to do it manually?

Karima - 2020-05-22

Hi,
I will reformulate my question maybe I will have an answer

does ELK code search the spin direction automatically in NCM calculations?

Andrew Shyichuk - 2020-05-22

Dear Karima,

There is no such feature in Elk. You'd have to do it manually.

Best regards.
Andrew

Andrew Shyichuk - 2020-05-22

Dear Karima,

There is no such feature in Elk. You'd have to do it manually.

Best regards.
Andrew

Karima - 2020-05-22

Dear Andrew
I applied a weak field 0.5 0 0 to orient the spin towards this direction ; the total resulting moment was obviously towards the direction of the field
after I restart a calculation based on the density of the old one (task 1) with "reducefb" option so the field has converged to another direction because the applied field has become negligible

what does this result mean?

I would be grateful to you for directing me

Andrew Shyichuk - 2020-05-23

Dear Karima,

Reducebf option gradually reduces the field on every iteration. The purpose is: use larger field to break symmetry, but then, gradually let the system to find the minimum without the field. The field becoming negligible is exactly the purpose of this keyword.

That, however, only works when the moment is stable without the field. That is not always the case. It happens that reducing the field also reduces the moment. Sometimes the system gets unphysical - zero total moment with odd number of electrons.

Thus, if you want a particular moment pointing in a particular direction - use fsmtype 1 and no reducedf.

If you want to freeze the moment at particular (correct) amplitude, and find its direction corresponding to energy minimum - you'd have to use fsmtype 1, no reducebf, and manually do many calculations in some range of directions (i.e. manual magnetocrystalline anisotropy search).

Update: If your system is small - try using SCAN meta-GGA and/or spin-orbit coupling.

Best regards.
Andrew