Hi Brad,
probably the calculation is not converged. Try a few things: 1) is the total energy at 2000Ry lower than at 200 Ry ? At self-consistency, it should be, even infinitesimally, due to the variaitonal principle. 2) try different recipes: cg vs davidson, and different initalizations (atomic+random, random, etccc). nicola Brad Malone wrote: > I happened to stumble upon something today that I thought was > unusual. The problem is illustrated in a simple example: if you take > the following basic cubic Si input file and, say, the Si.pz-vbc.UPF > pseudopotential from the QE website and do a test for convergence with > respect to ectutwfc. > > If we look at the 4 bands that are calculated we see the following > results: > > At ecutwfc=40 Ry: -5.1740 7.0370 7.0370 7.0370 > ecutwfc=100Ry: -5.1746 7.0369 7.0369 7.0369 > ecutwfc=200Ry: -5.1746 7.0369 7.0369 7.0369 > Now try > ecutwfc=2000Ry: -5.2862 6.9066 6.9066 10.2399 > > Now why do the values change? If I look at the output file for the > 2000 Ry case I see that there is a negative starting charge: > > Initial potential from superposition of free atoms > Check: negative starting charge= -0.057614 > > But still, why is this? The usual answer for a negative starting > charge is to increase the wavefunction cutoff, although I suspect > that's not the problem in this case..... > > So besides the using of a 2000 Ry cutoff for silicon, what else is > wrong here? > > Best, > Brad > UC Berkeley > > > &control > prefix = 'si' > calculation = 'scf' > restart_mode = 'from_scratch' > wf_collect = .false. > tstress = .true. > tprnfor = .true. > outdir = './' > wfcdir = './' > pseudo_dir = './' > / > &system > ibrav = 0 > celldm(1) = 10.2612 > nat = 2 > ntyp = 1 > nbnd = 4 > ecutwfc = 2000.0 > / > &electrons > electron_maxstep = 100 > conv_thr = 1.0d-10 > mixing_beta = 0.7 > diago_full_acc = .true. > / > CELL_PARAMETERS cubic > 0.000000000 0.500000000 0.500000000 > 0.500000000 0.000000000 0.500000000 > 0.500000000 0.500000000 0.000000000 > ATOMIC_SPECIES > Si 28.086 Si.pz-vbc.UPF > ATOMIC_POSITIONS crystal > Si -0.125000000 -0.125000000 -0.125000000 > Si 0.125000000 0.125000000 0.125000000 > K_POINTS automatic > 1 1 1 0 0 0 > > ------------------------------------------------------------------------ > > _______________________________________________ > 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