Dear Dan, I have seen this error in several cases particularly for transition metals and for basis and projector functions generated by our atompaw program. My understanding (based on a discussion with Stefano de Gironcoli) is that the program stops when the program detects a certain product of one-center terms to be negative. In my experience these terms can be negative before convergence and I have commented out the offending line. In my tests, this allows the program to converge consistently in the tests I have done. This is not necessarily safe or well-tested and I did promise to look into it further. In case you would like to also try, the offending line in 4.2.1 is line 553 in sct_mod.f90:
IF (okpaw) rho_ddot = rho_ddot + paw_ddot(rho1%bec, rho2%bec) I repeat that commenting out this line may not be a good idea, but it has worked for me in limited tests. (I still hope to do more tests.) Sincerely, Natalie Holzwarth N. A. W. Holzwarth email: natalie at wfu.edu Department of Physics web: http://www.wfu.edu/~natalie Wake Forest University phone: 1-336-758-5510 Winston-Salem, NC 27109 USA office: Rm. 300 Olin Physical Lab On Wed, Jul 6, 2011 at 5:54 AM, Dan Fors <forsdan at gmail.com> wrote: > Dear users, > > I am running a simple 2-atomic non-magnetic (NM) bcc Cr system (see > below for the input file) with v.4.2.1 and I keep getting an error > message regarding a negative dr2: > > from mix_rho : error # 1 > negative dr2 > > This error occurs for values close to as well as away from the > estimated equilibrium volume. What is the possible the origins of this > error and how may I eliminate it? > > I have tried to change the mixing_beta in the range 0.1 to 0.8, as > well as changing the mixing mode to 'TF'. I have also tried to set > nspin = 2 with a zero start magnetisation since an anti-ferromagnetic > (AFM) start configuration does not give rise to the problem (but > yields the AFM solution instead of the NM one). However. this also > gives the error. Finally, I tested to use ibrav = 3 and with only one > atom in the cell, but I still get the above error. > > What I have noticed is that in the AFM case I get a couple of very > flat bands in the bandstructure just above the Fermi level. If I > change to a USPP potential or an alternative PAW potential these bands > disappear, and the above error does not occur. Can the potential I use > in the present case be the source to the error, and if yes, what is > the reason behind it? > > I would appreciate any help or suggestions. > > Dan > > > > %------------------------------------- > > &CONTROL > calculation = 'scf', > restart_mode = 'from_scratch', > prefix = 'Cr', > tstress = .true., > tprnfor = .true., > pseudo_dir = > '/home/forsdan/PROGRAMS/QUANTUM_ESPRESSO/espresso-4.2.1_intel/pseudo/', > outdir = '/home/forsdan/FeCr_PROJECT/TEMP_PAW/' > / > &SYSTEM > ibrav = 1, celldm(1) = 5.378798, nat = 2, ntyp = 1, > ecutwfc = 40.0, ecutrho = 180.0, nbnd = 14 > occupations = 'smearing', > smearing = 'mp', degauss = 0.022, > nspin = 1, > / > &ELECTRONS > electron_maxstep = 100, > conv_thr = 1.0d-8, > diagonalization = 'cg', > mixing_mode = 'plain', > mixing_beta = 0.3 > / > ATOMIC_SPECIES > Cr 51.996 Cr.pbe-paw_kj_6.UPF > ATOMIC_POSITIONS {crystal} > Cr 0.00 0.00 0.00 > Cr 0.50 0.50 0.50 > K_POINTS {automatic} > 12 12 12 0 0 0 > > %------------------------------------- > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110706/dca1903f/attachment.htm