> 1) How to define whether a system is (or expected to be) insulating or > conducting by parameters of PWSCF?
You could start by using fractional occupations, and smearing, and see, after selfconsistency, if there is a gap or not. > 2) for metal/insulator supercell, how to set the related parameters? If > it's smearing, should I use a as small as possible smearing? Generally speaking, you want the result in the limit of zero smearing. In that limit, a metallic system will usually requires an extremely fine k-point sampling, since you are trying to integrate a discontinuous function. So, you need to find a smearing that is not too large to give you incorrect results, but large enough that you can use a reasonable number of k-points to achieve full sampling accuracy. See Chap 4 of http://quasiamore.mit.edu/phd for an introduction. Generally speaking, a smearing of 0.3eV=0.022Ry is a conservative starting points. PWscf uses Ry for smearing, CP (I believe) Ha. nicola --------------------------------------------------------------------- Prof Nicola Marzari Department of Materials Science and Engineering 13-5066 MIT 77 Massachusetts Avenue Cambridge MA 02139-4307 USA tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu
