On Wednesday 04 January 2006 17:32, Sergey Lisenkov wrote: > So, does it mean that it is not necessary to increase energy cutoff > (like at VASP, ABINIT - they use constant plane wave basis in variable > cell calculations) during vc-relax to get correct stress tensor?
if you use a constant plane-wave basis set, you have smooth results, but bad convergence with cutoff (due to "Pulay stress", i.e. the dependence of the basis set upon the volume). If you use a constant cutoff, you have better convergence with cutoff but "rough" stress (because the number of plane waves changes when the volume changes). With a suitable choice of parameters for the modified functional, you get smooth results with constant cutoff. More details are in the paper that was mentioned earlier. Paolo -- Paolo Giannozzi e-mail: giannozz at nest.sns.it Scuola Normale Superiore Phone: +39/050-509876, Fax:-563513 Piazza dei Cavalieri 7 I-56126 Pisa, Italy
