In data 22 aprile 2009 alle ore 10:17:02, Kun Yin <kyin.cn at gmail.com> ha scritto: > I don't quite understand this sentence. Just try to increase and decrease > default nr and nrs values as suggested. There are total 9 calculations, > 1-3 and 8-0 find symmetry right, 4-7 find symmetry wrong.
There is no symmetry "right" and "wrong", in calculations 4-7 pw.x does not use certain symmetry operations because they are not compatible with the FFT grid, this will make the calculation a more expensive (as the reduced number of k-points is higher), but not wrong. Let's do some number theory: > temp-1.out: G cutoff = 744.8786 ( 170271 G-vectors) FFT grid: > ( 80, 80, 80) > temp-2.out: G cutoff = 722.7847 ( 162825 G-vectors) FFT grid: > ( 80, 80, 80) > temp-3.out: G cutoff = 704.6276 ( 156325 G-vectors) FFT grid: > ( 80, 80, 80) > temp-4.out: G cutoff = 689.2743 ( 151669 G-vectors) FFT grid: > ( 75, 75, 75) > temp-5.out: G cutoff = 676.0151 ( 147349 G-vectors) FFT grid: > ( 75, 75, 75) > temp-6.out: G cutoff = 664.3728 ( 143471 G-vectors) FFT grid: > ( 75, 75, 75) > temp-7.out: G cutoff = 654.0170 ( 140255 G-vectors) FFT grid: > ( 75, 75, 75) > temp-8.out: G cutoff = 644.7053 ( 136787 G-vectors) FFT grid: > ( 72, 72, 72) > temp-9.out: G cutoff = 636.2575 ( 134435 G-vectors) FFT grid: > ( 72, 72, 72) 80 = 2^4 * 5 75 = 3 * 5^2 72 = 2^3 * 3^2 In other words, when the size of you FFT grid is not a multiple of 2 a certain symmetry operation canot be represented properly. You should be able to guess which operation it is from your atomic positions configuration. If I remember correctly symmetry is applied only on the FFT grid, the dimensions of the smooth grid should not matter. > For No. 5 calculation, defulat value is 75 and 48. I set nr1=nr2=nr3=80, > nr1s=nr2s=nr3s=50. It finds symmetry right! As consequence of what said above. Setting nrX=80 and leaving nrXs to their default values should also work. > when I decrease to nr1=nr2=nr3=72, nr1s=nr2s=nr3s=45. It reports error > and crash. Likely they are too small with respect to what your cutoffs requires! regards -- Lorenzo Paulatto SISSA & DEMOCRITOS (Trieste) phone: +39 040 3787 511 skype: paulatz www: http://people.sissa.it/~paulatto/ *** save italian brains *** http://saveitalianbrains.wordpress.com/