Hi sir, Thank you. I am trying to keep every setup the same in CP.x and Pw.x as you suggested. You mentioned that the k-points should be the same. But I cannot find the input card like &K_Points in cp.x, how could I control the k sampling? I only find the charge meshing commands like nr1...in &System. So I guess cp.x used some default setup or some different algorithm in MD calculation?
Best, Tian On Fri, Sep 14, 2012 at 7:30 AM, Paolo Giannozzi <giannozz at democritos.it>wrote: > On Thu, 2012-09-13 at 15:36 -0700, Tian Lan wrote: > > > But it seems that the energies that both codes obtained agree well. I > > pasted the results in the following. The first one is the result from > > vc-relax operated on one unit cell, the total energy is -358.1 Ry, > > this is very close to my original setup with scf calculation. The > > second one is from cp.x operated on 2 by 2 by 2 supercell, with fixed > > atom positions(ion and cell_dynamics are set to 'none'), the energy is > > -1410 au==-2820 Ry. I don't know whether this is a big difference > > the energy is -1431.80272 Ha or so, i.e. -1431.80272/8 Ha per cell, > i.e. 357.95Ry. Close (358.097) but not very close. Note however that > you need to compare equivalent results, i.e. same cell, same k-points, > or a cell and a supercell but with equivalent k-points. Also note > that the treatment of the augmentation charge via the "small boxes" > requires some testing in order to find a suitable value for input > variables nr1b, nr2b, nr3b. The resulting pressure may also change > quite a bit. > > > I don't quite get your point about the default positions of atoms in > > pw and cp. In both codes, I used 'crystal' > > perfect: it is of no concern for you. If you do not specify anything, > cp will assume borh radii and pw lattice parameters, or something > like this, as explained in the documentation > > P. > -- > Paolo Giannozzi, IOM-Democritos and University of Udine, Italy > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- Lan, Tian Ph.D. Candidate, Department of Applied Physics and Materials Science California Institute of Technology, Caltech M/C 138-78, Pasadena, CA, 91125 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120926/4272621e/attachment.htm
