Dear SIESTA users: I have used SIESTA to study the property of FePt systems.Here I have a question about the atomic forces SIESTA calculated: When I am calculating the FePt unit cell(including 4 atoms) with its lattice constant around 4 ang.The corresponding atomic forces are around 0.02 eV/ang.When I am using the 2x2x2 supercell(including 32 atoms) as unit cell, with relatively the same atomic positions,and the lattice constant is changed to 8 ang to maintain it is the same bulk as the previous one,however ,the atomic forces are increased to around one hundred eV/ang.
I also calculated another system using 3x3x3 supercell as unit cell, the forces are much even higher ,it seems the atomic force will increase with the number of atoms and the lattice constant. I am rather confused with its behavior,why there is such a drastic change in atomic forces and stress tensor while the bulk is the same, only the expression of it is different. I've attached both 1x1x1 and 2x2x2's input and output files,if needed. I really need your help. Thanks In Advance. & Best Wishes.. SuiYang 2006-11-21
FePt-1x1x1.out
Description: Binary data
FePt-1x1x1.fdf
Description: Binary data
FePt-2x2x2.out
Description: Binary data
FePt-2x2x2.fdf
Description: Binary data
