Thank Lorenzo, I did assure those settings. I can get identical energy. However, the x-y forces are not going to zero.
Duy ---------------------------------------------------- Duy Le Postdoctoral Associate Department of Physics University of Central Florida. Website: http://www.physics.ucf.edu/~dle On Wed, Nov 20, 2013 at 12:16 PM, Lorenzo Paulatto <lorenzo.paulatto at impmc.upmc.fr> wrote: > 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 > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum
