Dear Mohammad, This is quite likely due to Acoustic Sum Rules(ASR) if relaxation of the system is done correctly . Some negative frequencies may appear in vicinity of gamma point especially for 2D materials. These can be diminished by incresing nq1 and nq2 value in ph input file.
Bests 2017-07-22 11:23 GMT+03:00 Mohammad Alidoosti <[email protected]>: > > Dear PWSCF users, > > I am doing phonon frequencies calculations for Graphene-oxide. In > proximity to the Gamma point, I get small negative frequencies. As far as I > know this is a known problem, I have tried to increase "forc_conv_thr" and > "tr2_ph" to 1.0d-6 and 1.0d-16, respectively, but it doesn't work. Is there > any suggestion for solving this problem? > Hear is the scf input file : > ********************************************************************* > &control > title = GO > calculation = 'scf' > restart_mode = 'from_scratch' > prefix = 'GO-ph' > pseudo_dir = '/home/pseudo' > outdir = './tmp/' > nstep = 200 , > tstress = .true. , > tprnfor = .true. , > verbosity='high', > forc_conv_thr= 1.0d-6 > / > &system > ibrav = 0 > nat = 12 > ntyp = 3 > ecutwfc = 80 > ecutrho = 400 > occupations = 'smearing' > smearing='methfessel-paxton', > degauss = 0.001 > / > &electrons > conv_thr= 1.0d-8 > mixing_beta = 0.7 > electron_maxstep = 200, > / > &IONS > / > &CELL > cell_dofree = '2Dxy', > / > ATOMIC_SPECIES > C 12.0107 C.pbe-n-kjpaw_psl.0.1.UPF > O 15.999 O.pbe-n-kjpaw_psl.0.1.UPF > H 1.008 H.pbe-kjpaw_psl.0.1.UPF > CELL_PARAMETERS (angstrom) > 4.990235060 0.054948389 0.000000000 > -2.541880421 4.219875071 0.000000000 > 0.000000000 0.000000000 25.000000000 > > ATOMIC_POSITIONS (angstrom) > O -0.021826634 0.250928937 1.721705471 > H 0.809321037 0.681392784 1.997855886 > O -0.031523808 1.135550155 -1.892027240 > H 0.808877574 0.723408478 -2.168118129 > C 0.047350145 0.017290716 0.288486347 > C 0.032454255 1.370630042 -0.458840404 > C -1.237500438 2.119007372 -0.142173618 > C -1.224236423 3.485316018 -0.033121650 > C 1.242549808 3.515955831 -0.028144886 > C 1.285890831 2.150271662 -0.137183942 > C 2.528922921 1.430926894 -0.090219298 > C 2.544546281 0.011979550 -0.080086702 > K_POINTS automatic > 15 15 1 0 0 0 > ******************************************************************* > > Thanks in advance. > > Mohammad Alidoosti > -- > Institute for Research in Fundamental Sciences (IPM) > School of Nano-Science > Shahid Farbin Alley > Shahid Lavasani st > P.Code: 19538-33511 > Tehran, Iran > Tel: +98 21 2310 -3070 <+98%2021%202310%203070> > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > -- Bahadır SALMANKURT --- Ph.D. Candidate Department of Physics, Sakarya University, TURKEY --- Research Assistant Technology Faculty, Department of Information Systems Engineering, Kocaeli University, TURKEY Phone : +90 262 303 2208 <+90%20262%20303%2022%2008> Fax : +90 262 303 2203 <+90%20262%20303%2022%2003>
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