[Wien] why artificial lowering of symmetry changes the total energy?

[Stefaan Cottenier]

> {1} - (26 Pmc21)
> or
> {2} - (11 P21/m).
>
> The total FM energy of {1} is -152655.214439 Ry
>            and that of {2} is -152655.214842 Ry
>
> The precision of both calculations was 0.000001 Ry since all the figures after the point are important for me.
>
>   
That looks like a difference that is more than numerical noise. But: we 
should distinguish between accuracy and self-consistency. The precision 
of  0.000001 Ry which you quote is probably coming from your convergence 
criterium, isn't it? That means that your solution is considered to be 
self-consistent if such (strong) criterium is met. But that isn't the 
completely identical to requiring high absolute accuracy : your result 
can be highly self-consistent but not very accurate. And then it is not 
guaranteed that two formally identical cases will yield exactly the same 
energy. You can try to repeat these calculations with a higher RKmax, 
and see whether the energy difference decreases.

> I am including the case.dmatdn files of both cases. There are differences between the density matrices of {1} and {2}, but I do not know what they mean physically.
>
>   
These are 5x5 matrices, of which the diagonal elements correspond to the 
occupation of the different m-orbitals for d-electrons (roughly 
speaking...). At first sight, the diagonals look fairly identical in all 
cases. My bet is hence that you need a larger RKmax.

Stefaan


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