On 11/20/2013 05:54 PM, Duy Le wrote: > Dear all, > > I wonder if anyone knows how to vanish the forces acting on atoms in a > non-primitive cell. I saw that if I have 1x1x5 cell of Cu(111) (or any > other systems), the x-y components of forces are zero but when I make > 2x2x5 or other supercell, these forces becomes non-zero. Of course, > these values are quite small. I used lot of significant digits for > coordinates and cell parameters but they do not help.
To get exactly the same result for the bigger cell you must assure that the FFT grid scales proportionally and the K points grid scales inversely. I.e. lest say that the unit cell has nr1=10, nr2=10,nr3=10 (either specified by hand or automatically selected, it does not matter) and a 10x10x10 grid of k-points. If you build a 2x2x2 supercell you will have to check that nr1=20, nr2=20, nr3=20 and in case enforce it manually. You will also have to use 5x5x5 k-points, keeping in mind that if the grid was shifted it may be impossible to have exact equivalence. good work -- Dr. Lorenzo Paulatto IdR @ IMPMC -- CNRS & Universit? Paris 6 +33 (0)1 44 275 084 / skype: paulatz http://www-int.impmc.upmc.fr/~paulatto/ 23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 05
