Dear Jonathan, I am not sure if you tried, but the local-density-dependent TF screening is very important when the cell is large, like in your case. I did not find the PPs you are using in the quantum espresso webpage, so I downloaded the usual USPP and repeated the calculation. Here it is the input and the output that I obtained. It took a significant number of scf cycles to converge (more than 100, I had to restart the calculation), so probably a better optimization of the smearing/charge cutoff/etc... parameters can still be done. But considering it is Co-MgO we are talking about, I would say that it's ok. I hope it helps!
All best! Fabio Negreiros Ribeiro, Post-Doc, IPCF - Consiglio Nazionalle delle Ricerche, Pisa, Italy -----Original Message----- From: Jonathan Trinastic <[email protected]> To: pw_forum <pw_forum at pwscf.org> Sent: Tue, Mar 20, 2012 4:15 pm Subject: [Pw_forum] Problem with scf convergence Hi, I'm having an issue getting a Co-MgO interface to converge properly. Basically, the setup includes 8 layers of bcc Co interfaced with 8 layers of MgO, periodic in x and y and a vacuum between interfaces in the z direction. I'm trying to find the Co-O distance that gives the energy minimum, so I'm trying to relax structures with varying distances - I'm using a 2.17 A distance to start based on experimental values. I've been able to relax the Co and MgO parts separately without a problem, but when I combine them they won't converge. I've included my pw.x input below, however I have also tried adjust many of the parameters based on feedback in other posts and the QE User guide, such as: increasing degauss or adding bands to account for metallic nature of Co, decreasing mixing beta, increasing the energy cutoff value, however all these end up having the same convergence problems where the estimated scf accuracy hovers around 1-10. Does anyone see potential issues with the input I'm using that I'm missing? I've chosen my energy and charge density cutoffs based on the recommended choices for the oxygen PAW potential, which is higher than for Co or Mg. Thanks, Jonathan &control calculation='scf', restart_mode='from_scratch', pseudo_dir = '/scratch/hpc/jptrinas/espresso-4.3.2/pseudo/', outdir='./tmp/' prefix='bcc.co.mgo' tstress = .true. tprnfor = .true. / &system ibrav = 6, celldm(1) =5.32, celldm(3) = 19.52, nat= 24, ntyp= 3 starting_magnetization(1)=0.7, nspin=2 ecutwfc = 38.0, ecutrho = 151.0 occupations='smearing', smearing='gaussian', degauss=0.02 / &electrons diagonalization='cg' conv_thr = 1.0e-6 mixing_beta = 0.3 / ATOMIC_SPECIES Co 58.93 Co.pbe-p-paw.UPF Mg 24.31 Mg.pbe-nsp-bpaw.UPF O 15.99 O.pbe-kjpaw.UPF ATOMIC_POSITIONS (alat) Co 0.0 0.0 5.000 Co 0.5 0.5 5.500 Co 0.0 0.0 6.000 Co 0.5 0.5 6.500 Co 0.0 0.0 7.000 Co 0.5 0.5 7.500 Co 0.0 0.0 8.000 Co 0.5 0.5 8.500 O 0.5 0.5 9.270 Mg 0.0 0.0 9.270 O 0.0 0.0 10.02 Mg 0.5 0.5 10.02 O 0.5 0.5 10.77 Mg 0.0 0.0 10.77 O 0.0 0.0 11.52 Mg 0.5 0.5 11.52 O 0.5 0.5 12.27 Mg 0.0 0.0 12.27 O 0.0 0.0 13.02 Mg 0.5 0.5 13.02 O 0.5 0.5 13.77 Mg 0.0 0.0 13.77 O 0.0 0.0 14.52 Mg 0.5 0.5 14.52 K_POINTS (automatic) 6 6 1 0 0 0 Typical scf accuracy estimates by end of run: estimated scf accuracy < 16.36480484 Ry estimated scf accuracy < 8.36686889 Ry estimated scf accuracy < 2.33384573 Ry estimated scf accuracy < 6.92471882 Ry estimated scf accuracy < 13.18681083 Ry estimated scf accuracy < 11.95347196 Ry estimated scf accuracy < 11.49117957 Ry estimated scf accuracy < 12.65621865 Ry estimated scf accuracy < 8.53355241 Ry estimated scf accuracy < 6.20738100 Ry estimated scf accuracy < 7.91117866 Ry estimated scf accuracy < 17.89939870 Ry estimated scf accuracy < 4.29389382 Ry estimated scf accuracy < 8.11074063 Ry estimated scf accuracy < 3.91904239 Ry estimated scf accuracy < 2.99042194 Ry estimated scf accuracy < 2.47072016 Ry estimated scf accuracy < 5.16323880 Ry estimated scf accuracy < 4.17983416 Ry estimated scf accuracy < 16.77910831 Ry estimated scf accuracy < 8.52666365 Ry estimated scf accuracy < 4.02303973 Ry estimated scf accuracy < 11.00391780 Ry estimated scf accuracy < 4.89255713 Ry -- Jonathan Trinastic, M.S. Graduate Student Department of Physics University of Florida _______________________________________________ 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/20120320/7503c053/attachment-0001.htm -------------- next part -------------- A non-text attachment was scrubbed... Name: input.in Type: application/octet-stream Size: 1241 bytes Desc: not available Url : http://www.democritos.it/pipermail/pw_forum/attachments/20120320/7503c053/attachment-0002.obj -------------- next part -------------- A non-text attachment was scrubbed... Name: input.out Type: application/octet-stream Size: 98324 bytes Desc: not available Url : http://www.democritos.it/pipermail/pw_forum/attachments/20120320/7503c053/attachment-0003.obj
