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 scalethe atom coordinates with lattice parameter, but in fact you don't).Best regardsAndrei Postnikov ----- Francisco Garcia <garcia.ff....@gmail.com> 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?
-- SIESTA is supported by the Spanish Research Agency (AEI) and by the European H2020 MaX Centre of Excellence (http://www.max-centre.eu/)