<div dir="ltr"><div>Dear Mohammad,</div><div><br></div>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. <div><br></div><div>Bests</div><div class="gmail_extra"><br><div class="gmail_quote">2017-07-22 11:23 GMT+03:00 Mohammad Alidoosti <span dir="ltr"><<a href="mailto:m.alidoosti@gmail.com" target="_blank">m.alidoosti@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><br clear="all"><div>Dear PWSCF users,</div><div><br></div><div>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?</div><div>Hear is the scf input file : </div><div>******************************<wbr>******************************<wbr>*********</div><div><div> &control</div><div> title = GO</div><div> calculation = 'scf'<span style="white-space:pre-wrap"> </span></div><div> restart_mode = 'from_scratch'<span style="white-space:pre-wrap"> </span></div><div> prefix = 'GO-ph'</div><div> pseudo_dir = '/home/pseudo'</div><div> outdir = './tmp/'<span style="white-space:pre-wrap"> </span></div><div> nstep = 200 , </div><div> tstress = .true. ,</div><div> tprnfor = .true. ,</div><div> verbosity='high',</div><div> forc_conv_thr= 1.0d-6</div><div> /</div><div> &system</div><div> ibrav = 0<span style="white-space:pre-wrap"> </span> </div><div> nat = 12<span style="white-space:pre-wrap"> </span></div><div> ntyp = 3<span style="white-space:pre-wrap"> </span></div><div> ecutwfc = 80<span style="white-space:pre-wrap"> </span></div><div> ecutrho = 400</div><div> occupations = 'smearing'<span style="white-space:pre-wrap"> </span></div><div> smearing='methfessel-paxton', </div><div> degauss = 0.001</div><div>/</div><div> &electrons</div><div>conv_thr= 1.0d-8</div><div>mixing_beta = 0.7</div><div> electron_maxstep = 200,<span style="white-space:pre-wrap"> </span></div><div> /</div><div> &IONS</div><div>/</div><div>&CELL</div><div>cell_dofree = '2Dxy',</div><div>/</div><div>ATOMIC_SPECIES</div><div> C 12.0107 C.pbe-n-kjpaw_psl.0.1.UPF</div><div> O 15.999 O.pbe-n-kjpaw_psl.0.1.UPF</div><div> H 1.008 H.pbe-kjpaw_psl.0.1.UPF</div><div>CELL_PARAMETERS (angstrom)</div><div> 4.990235060 0.054948389 0.000000000</div><div> -2.541880421 4.219875071 0.000000000</div><div> 0.000000000 0.000000000 25.000000000</div><div><br></div><div>ATOMIC_POSITIONS (angstrom)</div><div>O -0.021826634 0.250928937 1.721705471</div><div>H 0.809321037 0.681392784 1.997855886</div><div>O -0.031523808 1.135550155 -1.892027240</div><div>H 0.808877574 0.723408478 -2.168118129</div><div>C 0.047350145 0.017290716 0.288486347</div><div>C 0.032454255 1.370630042 -0.458840404</div><div>C -1.237500438 2.119007372 -0.142173618</div><div>C -1.224236423 3.485316018 -0.033121650</div><div>C 1.242549808 3.515955831 -0.028144886</div><div>C 1.285890831 2.150271662 -0.137183942</div><div>C 2.528922921 1.430926894 -0.090219298</div><div>C 2.544546281 0.011979550 -0.080086702</div><div>K_POINTS automatic<span style="white-space:pre-wrap"> </span> </div><div>15 15 1 0 0 0</div></div><div>******************************<wbr>******************************<wbr>*******</div><div><br></div><div>Thanks in advance.</div><span class="gmail-m_-4665353229066929847HOEnZb"><font color="#888888"><div><br></div><div>Mohammad Alidoosti</div>-- <br><div class="gmail-m_-4665353229066929847m_-4630381792783031416gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div style="margin-bottom:0px;margin-left:0px;padding-bottom:5px"><div><div dir="ltr"><div><div dir="ltr"><font><span style="font-family:arial,helvetica,sans-serif"><font color="#888888" style="font-size:12.8px">Institute for Research in Fundamental Sciences (IPM)</font><br><font color="#888888" style="font-size:12.8px">School of Nano-Science</font><br><font color="#888888" style="font-size:12.8px">Shahid Farbin Alley</font><br><font color="#888888" style="font-size:12.8px">Shahid Lavasani st</font></span></font></div><div dir="ltr"><font><span style="font-family:arial,helvetica,sans-serif"><font color="#888888">P.Code: 19538-33511</font></span></font></div><div dir="ltr"><font><span style="font-size:12.8px;color:rgb(136,136,136);font-family:arial,helvetica,sans-serif">Tehran, Iran</span><span style="font-family:arial,helvetica,sans-serif"><font color="#888888"><br></font></span></font></div><div dir="ltr"><font><span style="font-family:arial,helvetica,sans-serif"><font color="#888888" style="font-size:12.8px">Tel: </font><font size="2" color="#999999"><a href="tel:+98%2021%202310%203070" value="+982123103070" target="_blank">+98 21 2310 -3070</a></font><br></span></font></div><div style="font-size:12.8px;color:rgb(136,136,136)"><font color="#888888"><span style="font-family:arial,helvetica,sans-serif"><br></span></font></div></div></div><div style="font-size:12.8px"></div></div></div><div style="font-size:12.8px"></div></div></div></div></div></div></div></div></div></div></div></div></div>
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