Thanks for your responses. I figured out my errors. The problem has been

On Mon, Mar 28, 2022 at 3:50 PM Andrei Postnikov <> wrote:

> Dear Francisco:
> as a general statement, your expectation is justified. However, unexpected
> things happen.
> Having posted an (input) / output file would help to pinpoint a problem.
> Without any additional information, I'd guess that your lattice vectors
> are not exactly fcc,
> or the atoms are not exactly at symmetric positions. (E.g., you think that
> you scale
> the atom coordinates with lattice parameter, but in fact you don't).
> Best regards
> Andrei Postnikov
> ----- Francisco Garcia <> a écrit :
> >
> Dear Users
> I performed a series of single point energy calculations on an FCC crystal
> by varying the lattice constant. I'm trying to generate data points to
> optimize the lattice constant
> I was expecting the force on each atom to zero by virtue of crystalline
> symmetry (no internal degree of freedom). But to my surprise, the forces
> are not zero. Increasing the Mesh cutoff from 300 Ry to higher values
> didn't help either. How is it possible for the atomic forces in a crystal
> to be non-zero?
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