Short-range order correction in sqs2tdb

Alloy Theoretic Automated Toolkit (ATAT)
1

Hi all,

For the short-range order correction when using sqs2tdb “-fit -sro” option, I am not sure whether I understand it correctly:

We only apply the SRO corrections to single-sublattice systems, as it would compensate for
the lack of long-range order in solid solution of single-sublattice phases; otherwise, the long-range order effects in multi-sublattice structures would bring out energetic advantages. Therefore, for a phase diagram with only single-sublattice phases (like Pt-W phase diagram with only FCC+BCC), SRO corrections are not necessary. However, if the system does not contain multi-sublattice phases, but a liquid phase calculated with MD (like Pt-W with BCC+FCC+Liquid), we still need an SRO correction, since the liquid phase energy calculated with MD contains SRO effects.

2

I agree with the the last statement, it’s a very good idea to include SRO effects for the solid if your liquid free energy comes from MD.
The first statement about “not needing” SRO correction if there are only single-sublattice phases is not as sure. The SRO can change the shape of the free energy enough to make a difference (it’s just a smaller effect than if there are ordered phases).