Dear Neel,
there is no difference. You can specify the size of your unit cell using different units of measure, but provided you convert your units correctly, you will of course have the same unit cell, and same computational cost. Of course you can use larger cells that contain multiples of the primitive unit cell, and this a larger "nat" and a larger computational cost. Suggestion - before proceeding further with the code, try to study silicon using a 2-atom fcc unit cell, specifying atomic positions in any of the possible modes, and checking that the results and the computational time does not change. nicola Neel Singh wrote: > HI 2 all, > > I have a doubt. Please help me, i will be very thankful to all of you. > When we define our system in terms of atomic positions, we have four > option like bohr, angstrom etc. I want to know weather the > computational time will be less when we describe any crystal structure > in option crystal (atomic positions {crystal}) as compared to > angstrom/bohr(atomic positions {angstrom}) as the parameters nat > (number of atoms) in &system will less in crystal option as compared > to angstrom/bohr option. > > Thanks > > Neel Singh > University of Delhi, > India > > > ------------------------------------------------------------------------ > Love Cricket? Check out live scores, photos, video highlights and > more. Click here > <http://in.rd.yahoo.com/tagline_cricket_2/*http://cricket.yahoo.com>. > ------------------------------------------------------------------------ > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- --------------------------------------------------------------------- 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