Dear Lorenzo and Gabriele, Thank you very much for your suggestions. I will try them out.
Regards, Manoj On Fri, 9 Oct 2009, Gabriele Sclauzero wrote: > > > Manoj Srivastava wrote: > > Dear users, > > Thank you all for quick reply. Through all the replies I am under the > > impression that the forces can never be actually zero, even for perfect > > FCC lattice. I dont know the exact reason yet, whether it is just > > numerical or something bad on my side. So, I would like to give it one > > more shot, and i have some questions on that. > > > > Duy Le: I will try using crystal and report to the forum. Although > > relaxation stops after completing one scf cycle, so atoms actually dont > > move, but still nonzero forces. > > > > S. Baroni: When you use cubic symmetry, do you get forces on all atoms > > zero. Did you do the calculation or is this your intution? also, can one > > use cubic symmetry for low symmetry unit cell as in my case? > > As I wrote you in my previous mail, it is not that you use cubic symmetry, > but you start > from cubic symmetry operations to find the actual symmetries (by removing > those which do > not hold anymore depending on the lattice and atomic positions). > You could do the exercise to find out by hand what the symmetry should be in > your case and > check that the symmetry operations correspond to those found by pw.x > > > > > > which is also one order of magnitude smaller than before, so i am > > guessing there might me some other parameters that are not set up > > correctly and causing symmetry breaking? Would someone mind to tell me? I > > dont know much about FFT grid, Isn't FFT dimension determined by the KE > > cutoff? Is there anyother way of changing it? > > I don't know what the cause could be, anyway, since you seem to be very > curious and to > have some spare time for testing, I can suggest the following: in forces.f90 > uncomment the > section between #if defined (DEBUG) and #endif and look at the various > contributions to > the forces (this is present in the CVS version, I don't know if also in the > released one). > By looking at the single terms you might find why they do not cancel exactly. > > Cheers > > GS > > > > > Regards, > > Manoj Srivastava > > University of Florida > > Gainesville, FL > > > > -- > > > o ------------------------------------------------ o > | Gabriele Sclauzero, PhD Student | > | c/o: SISSA & CNR-INFM Democritos, | > | via Beirut 2-4, 34014 Trieste (Italy) | > | email: sclauzer at sissa.it | > | phone: +39 040 3787 511 | > | skype: gurlonotturno | > o ------------------------------------------------ o > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >