Dear Paolo, Using the following input, I did two calculations, once at gamma point only, and once with 4 4 3 0 0 0 K-sampling, to calculate the bandgap of ZnS (a semiconductor with a direct gap at gamma point)
/ &SYSTEM ibrav = 4 A = 3.811 C = 6.234 nat = 4 ntyp = 2 nbnd = 19 ecutwfc = 80 / &ELECTRONS / ATOMIC_SPECIES Zn 65.409 Zn.pbe-nc.UPF S 32.066 S.pbe-n-nc.UPF ATOMIC_POSITIONS crystal Zn 0.33333 0.66667 0.000 Zn 0.66667 0.33333 0.500 S 0.33333 0.66667 0.375 S 0.66667 0.33333 0.875 K_POINTS automatic OR K_POINTS gamma 4 4 3 0 0 0 For gamma only calculation, I have the following band energies: k = 0.0000 0.0000 0.0000 ( 3194 PWs) bands (ev): -5.6961 -4.6015 -0.1027 -0.1027 -0.0711 -0.0495 -0.0495 0.2414 0.2414 0.3243 0.3243 0.5610 1.6809 6.5472 6.5474 7.4256 7.5926 7.5926 9.2391 highest occupied, lowest unoccupied level (ev): 7.5926 9.2391 For 4 4 3 0 0 0 sampling, I got the followings: k = 0.0000 0.0000 0.0000 ( 6387 PWs) bands (ev): -6.6872 -5.7232 0.0468 0.0574 0.0574 0.1373 0.1373 0.4912 0.4913 0.5680 0.5680 0.7323 1.1728 5.6554 5.6556 6.5171 6.5888 6.5888 8.6817 highest occupied, lowest unoccupied level (ev): 6.5888 8.6817 In both cases the gap occurs at gamma point, however, the numbers are different. How should I explain this? Thanks in advance, On Wed, Dec 19, 2012 at 5:41 AM, Paolo Giannozzi <giannozz at democritos.it>wrote: > > On Dec 19, 2012, at 11:28 , Giuseppe Mattioli wrote: > > > Always negligible experimental measurements (i.e., vox populi)? :-) > > experiments are made on real semiconductors, not on theoretical > ones ... > > P. > --- > Paolo Giannozzi, Dept of Chemistry&Physics&Environment, > Univ. Udine, via delle Scienze 208, 33100 Udine, Italy > Phone +39-0432-558216, fax +39-0432-558222 > > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- *************************************** Amin Torabi Ph.D. student Chemistry Dept. The University of Western Ontario London, On Canada, N6A 5B7 Phone: 519-661-2111 Ext: 87871 **************************************** -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20130127/3eb56d21/attachment.html