# How would you report the lattice parameters of an alloy, modelled using a supercell

There is a whole lot of literature behind ab initio modelling of alloys with statistical site occupancies. These include VCA, SQS, CPA, supercell approach, etc. This question does not aim to compare these approaches, but it rather assumes a case where the supercell approach is used to model a new alloy using the DFT framework.

Consider some alloy $$\ce{A_{0.33}B_{0.67}C3}$$. A supercell of size 1x1x3 (it's small, but for the sake of understanding) is generated and the geometry optimisation is performed.

Now, I have two questions.

1. During the supercell generation, the space group symmetry of the original alloy can be (is probably) lowered, because the supercell may not support the same amount of symmetry operations. Therefore, how plausible is it to report the symmetry of the optimised supercell as the final relaxed symmetry of the original alloy? Are there any strategies to go back to the original unit cell from a relaxed supercell?
2. What is the convention when reporting the optimised lattice parameters? Do you report the parameters as they are for the supercell ~(a, b, 3c), or do you take the average ~(a, b, cavg)?
• I think it will depend on what type of lattice are you reporting: the primitive or the non-primitive unit cell. – Camps Aug 16 '20 at 13:40