<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div>>Then, may I make a conclusion that this structure or composition is unstable?</div><div> <br>If you have imaginary frequency, yes. If the structure is a high temperature phase, it is another story. DFPT works at low temperatures (strongly speaking at T=0K).<br><br>Bests,<br>Eyvaz.<br></div><div>-------------------------------------------------------------------<br>Prof. Eyvaz Isaev, <br>Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden <br>Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, <br>isaev@ifm.liu.se, eyvaz_isaev@yahoo.com<br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Arial"
size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> GAO Zhe <flux_ray12@163.com><br><b><span style="font-weight: bold;"> </span></b></font> .<br><div id="yiv1336422892"><div style="line-height: 1.7; color: rgb(0, 0, 0); font-size: 14px; font-family: arial;">I have obtained the convergent result by decreasing alpha_mix(1) from 0.7 to 0.4. But the result has imaginary frequency (about -80 cm^-1) at X(100).<br>Further more, I also tried VCA (by virtual.x) +DFPT method for the same composition and strucutre, X(100) still had imaginary frequency (also about -80 cm^-1).<br>Then, may I make a conclusion that this structure or composition is unstable?<br>Looking forward to your reply.<br>Best Regards.<br><div>--<br>GAO Zhe<br>CMC Lab, MSE, SNU, Seoul, S.Korea<br>
</div><br>At 2011-07-17 15:39:13,"Eyvaz Isaev" <eyvaz_isaev@yahoo.com> wrote:<br> <blockquote id="yiv1336422892isReplyContent" style="padding-left: 1ex; margin: 0px 0px 0px 0.8ex; border-left: 1px solid rgb(204, 204, 204);"><div style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-family: times new roman,new york,times,serif; font-size: 12pt;"><div>> I was not sure whether this problem caused by empty-band number, so I increase nbnd.</div><div> <br>You should increase nbnd if you see "too few bands" message in *.ph.out file. <br><br>Bests,<br>Eyvaz. <br> <br></div><div> <br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Arial" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> GAO Zhe <<a rel="nofollow" ymailto="mailto:flux_ray12@163.com"
target="_blank" href="mailto:flux_ray12@163.com">flux_ray12@163.com</a>><br><b><span style="font-weight: bold;">To:</span></b> Eyvaz Isaev <<a rel="nofollow" ymailto="mailto:eyvaz_isaev@yahoo.com" target="_blank" href="mailto:eyvaz_isaev@yahoo.com">eyvaz_isaev@yahoo.com</a>>; PWSCF Forum <<a rel="nofollow" ymailto="mailto:pw_forum@pwscf.org" target="_blank" href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br><b><span style="font-weight: bold;">Sent:</span></b> Sunday, July 17, 2011 11:33 AM<br><b><span style="font-weight: bold;">Subject:</span></b> Re:
[Pw_forum] ph.x cannot reach convergence within 100 steps<br></font><br><div id="yiv1336422892">Thank you very much, Prof. Isaev.<br>I tried all of 'scf', 'relax' and 'vc-relax' before ph.x, but got the same problem in each case~<br>I was not sure whether this problem caused by empty-band number, so I increase nbnd. It may too large for my model~ Now, I am trying to change the values of alpha_mix(1) and nmix_ph for a better convergent.<br>Thank you, again ^_^<br><div>--<br>GAO Zhe<br>CMC Lab, MSE, SNU, Seoul, S.Korea<br>
</div><br>At 2011-07-16 16:39:40，"Eyvaz Isaev" <<a rel="nofollow" ymailto="mailto:eyvaz_isaev@yahoo.com" target="_blank" href="mailto:eyvaz_isaev@yahoo.com">eyvaz_isaev@yahoo.com</a>> wrote:<br> <blockquote id="yiv1336422892isReplyContent" style="padding-left: 1ex; margin: 0px 0px 0px 0.8ex; border-left: 1px solid rgb(204, 204, 204);"><div style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-family: times new roman,new york,times,serif; font-size: 12pt;"><div>Hi, <br></div><div><br></div><div>>Recently, I am trying to calculate phonon dispersion via ph.x. However,
in some cases, ph.x cannot reach convergence within 100 steps and stop
>automaticly.</div><div> <br>1. You should perform 'scf', not 'vc-relax' before phonon calculations.<br>2. You have a rather large system (nbnd=100), but used alpha_mix(1) by default (0.7). Try it around 0.1.<br>3. Try changing nmix_ph (by default 4).<br>4. If this does not help change 'maxter=100' in phcom.f90 and recompile.<br><br>Bests,<br>Eyvaz.<br><br></div><div>-------------------------------------------------------------------<br>Prof. Eyvaz Isaev, <br>Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden <br>Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, <br><a rel="nofollow" ymailto="mailto:isaev@ifm.liu.se" target="_blank" href="mailto:isaev@ifm.liu.se">isaev@ifm.liu.se</a>, <a rel="nofollow" ymailto="mailto:eyvaz_isaev@yahoo.com" target="_blank" href="mailto:eyvaz_isaev@yahoo.com">eyvaz_isaev@yahoo.com</a><br></div><div style="font-family: times new roman,new
york,times,serif; font-size: 12pt;"><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Arial" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b>
GAO Zhe <<a rel="nofollow" ymailto="mailto:flux_ray12@163.com" target="_blank" href="mailto:flux_ray12@163.com">flux_ray12@163.com</a>><br><b><span style="font-weight: bold;">To:</span></b> PWSCF Forum <<a rel="nofollow" ymailto="mailto:pw_forum@pwscf.org" target="_blank" href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br><b><span style="font-weight: bold;">Sent:</span></b> Saturday, July 16, 2011 7:40 AM<br><b><span style="font-weight: bold;">Subject:</span></b> [Pw_forum] ph.x cannot reach convergence within 100 steps<br></font><br><div id="yiv1336422892">Dear QE developer and users:<br>Recently, I am trying to calculate phonon dispersion via ph.x. However, in some cases, ph.x cannot reach convergence within 100 steps and stop automaticly.<br>I have tested the convergent lattice parameter, cut-off energy and k-points (M-P grid), and the thresholds of force and stress were also very low. Even if I increase the tr2_ph from
1.0d-12 (default) to 1.0d-10, the |ddv_scf|^2 values was around 10^(-6) or 10^(-7) magnitude. The problem usually occurred at the second q-point, but sometimes, even if lucky enough, it would definitely occur at
the third q-point (4 q-points in 3x3x3 case).<br>Are there any methods to solve this problem? Any suggestion will be welcome.<br>Calculations were used GGA-PBE USPP.<br>This is my input file:<br><i>cat >W25.relax.in <<EOF<br>&control<br> calculation = 'vc-relax' ,<br> disk_io = 'low' ,<br> prefix = 'W' ,<br> outdir = '$TempDIR/' ,<br> pseudo_dir = '$PseudoDIR/' ,<br> etot_conv_thr = 1.0d-12 ,<br> forc_conv_thr = 1.0d-4 ,<br>/<br>&system<br> ibrav = 1 ,<br> celldm(1) = ******* ,<br> nat = ** ,<br> ntyp = 3 ,<br> nbnd = 100 ,<br> ecutwfc = 47.5 ,<br> ecutrho = 450 ,<br> occupations =
'smearing' ,<br> smearing = 'mp' ,<br> degauss = 0.003 ,<br>/<br>&electrons<br> conv_thr = 1.0d-12 ,<br> startingpot = 'atomic' ,<br> startingwfc = 'atomic+random' ,<br> diagonalization = 'cg' ,<br> electron_maxstep = 150 ,<br>/<br>&ions<br> ion_dynamics = 'bfgs' ,<br>/<br>&cell<br> cell_dynamics = 'bfgs' ,<br> press_conv_thr = 0.01 ,<br>/<br>ATOMIC_SPECIES<br> V 50.9415 V.pbe-n-van.UPF<br> W 183.800 W.pbe-nsp-van.UPF<br> C 12.0110 C.pbe-van_ak.UPF<br>ATOMIC_POSITIONS crystal<br> V 0.50 0.50 0.00<br>...........<br> C 0.50 0.50 0.50<br>K_POINTS
automatic<br>13 13 13 0 0 0<br>EOF<br>echo -e " Relaxing Structure...\c"<br>$MPIBIN/mpirun -n 6 pw.x -npool 2 <W.relax.in >W.relax.out<br>echo -e " DONE"<br><br>cat >W.ph.in <<EOF<br>Phonon Calculation<br>&inputph<br> outdir = '$TempDIR/' ,<br> prefix = 'W' ,<br> ldisp = .true. ,<br> nq1 = 3 ,<br> nq2 = 3 ,<br> nq3 = 3 ,<br> tr2_ph = 1.0d-10 ,<br> fildyn = 'W.dyn' ,<br>/<br>EOF<br>echo -e " Calculating Dynamic Matrix...\c"<br>$MPIBIN/mpirun -n 6 ph.x -npool 2 <W.ph.in >W.ph.out<br>echo -e " DONE"</i><br>
<br><br><div>--<br>GAO Zhe<br>CMC Lab, MSE, SNU, Seoul, S.Korea<br>
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