Lattice energy optimisation

Dear Prof. Gale,

I am studying the effect of mechanical properties of a material by varying the composition of the element that is to be substituted.

I achieve lattice energy optimisation for all compositions between 0 and 1, except for 0.1. Gnorm for the same is 0.19

In this case , can I consider this result. Just wondering, how it works for all except 0.1.

Kindly clarify.

If an optimisation fails then you need to find out why & fix it otherwise the result is no good. Chances are there is a cutoff discontinuity in the force field you are using, as this is the number one cause of optimisation failures.

Thank you Prof.Gale for the clarification.

I have an other doubt too. When should we include symmetry and when should we not , while doing defect calculations.

The symmetry is defined by the structure you input, regardless of whether it is used or not. The only thing to remember is that a low symmetry structure can optimise to a high symmetry one, but not vice versa.