>Then,? may I make a conclusion that this structure or composition is unstable? ? 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).
Bests, Eyvaz. ------------------------------------------------------------------- Prof. Eyvaz Isaev, Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com ________________________________ From: GAO Zhe <[email protected]> ? . 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). 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). Then,? may I make a conclusion that this structure or composition is unstable? Looking forward to your reply. Best Regards. -- GAO Zhe CMC Lab, MSE, SNU, Seoul, S.Korea At 2011-07-17 15:39:13,"Eyvaz?Isaev"?<eyvaz_isaev at yahoo.com> wrote: > I was not sure whether this problem caused by empty-band number, so I > increase nbnd. >? >You should increase nbnd if you see "too few bands" message? in *.ph.out file. > >Bests, >Eyvaz. >? > >? > > >________________________________ >From: GAO Zhe <flux_ray12 at 163.com> >To: Eyvaz Isaev <eyvaz_isaev at yahoo.com>; PWSCF Forum <pw_forum at pwscf.org> >Sent: Sunday, July 17, 2011 11:33 AM >Subject: Re: [Pw_forum] ph.x cannot reach convergence within 100 steps > > >Thank you very much, Prof. Isaev. >I tried all of 'scf', 'relax' and 'vc-relax' before ph.x, but got the same >problem in each case~ >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. >Thank you, again ^_^ > >-- >GAO Zhe >CMC Lab, MSE, SNU, Seoul, S.Korea > >At 2011-07-16 16:39:40?"Eyvaz?Isaev"?<eyvaz_isaev at yahoo.com> wrote: > >Hi, >> >> >> >>>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. >>? >>1. You should? perform 'scf', not 'vc-relax' before phonon calculations. >>2. You have a rather large system (nbnd=100), but used alpha_mix(1) by >>default (0.7). Try it around 0.1. >>3. Try changing nmix_ph (by default 4). >>4. If this does not help change 'maxter=100' in phcom.f90 and recompile. >> >>Bests, >>Eyvaz. >> >> >>------------------------------------------------------------------- >>Prof. Eyvaz Isaev, >>Department of Physics, Chemistry, and Biology (IFM), Linkoping University, >>Sweden >>Theoretical Physics Department, Moscow State Institute of Steel & Alloys, >>Russia, >>isaev at ifm.liu.se, eyvaz_isaev at yahoo.com >> >> >>________________________________ >>From: GAO?Zhe <flux_ray12 at 163.com> >>To: PWSCF Forum <pw_forum at pwscf.org> >>Sent: Saturday, July 16, 2011 7:40 AM >>Subject: [Pw_forum] ph.x cannot reach convergence within 100 steps >> >> >>Dear QE developer and users: >>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. >>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). >>Are there any methods to solve this problem? Any suggestion will be welcome. >>Calculations were used GGA-PBE USPP. >>This is my input file: >>cat >W25.relax.in <<EOF >>&control >>???? calculation = 'vc-relax' , >>???? disk_io = 'low' , >>???? prefix = 'W' , >>???? outdir = '$TempDIR/' , >>???? pseudo_dir = '$PseudoDIR/' , >>???? etot_conv_thr = 1.0d-12 , >>???? forc_conv_thr = 1.0d-4 , >>/ >>&system >>???? ibrav = 1 , >>???? celldm(1) = ******* , >>???? nat = ** , >>???? ntyp = 3 , >>???? nbnd = 100 , >>???? ecutwfc = 47.5 , >>???? ecutrho = 450 , >>???? occupations = 'smearing' , >>???? smearing = 'mp' , >>???? degauss = 0.003 , >>/ >>&electrons >>???? conv_thr = 1.0d-12 , >>???? startingpot = 'atomic' , >>???? startingwfc = 'atomic+random' , >>???? diagonalization = 'cg' , >>???? electron_maxstep = 150 , >>/ >>&ions >>???? ion_dynamics = 'bfgs' , >>/ >>&cell >>???? cell_dynamics = 'bfgs' , >>???? press_conv_thr = 0.01 , >>/ >>ATOMIC_SPECIES >>? V?? 50.9415?? V.pbe-n-van.UPF >>? W?? 183.800?? W.pbe-nsp-van.UPF >>? C?? 12.0110?? C.pbe-van_ak.UPF >>ATOMIC_POSITIONS crystal >>? V?? 0.50? 0.50? 0.00 >>........... >>? C?? 0.50? 0.50? 0.50 >>K_POINTS automatic >>13? 13? 13?? 0? 0? 0 >>EOF >>echo -e "? Relaxing Structure...\c" >>$MPIBIN/mpirun -n 6 pw.x -npool 2 <W.relax.in >W.relax.out >>echo -e " DONE" >> >>cat >W.ph.in <<EOF >>Phonon Calculation >>&inputph >>???? outdir = '$TempDIR/' , >>???? prefix = 'W' , >>???? ldisp = .true. , >>???? nq1 = 3 , >>???? nq2 = 3 , >>???? nq3 = 3 , >>???? tr2_ph = 1.0d-10 , >>???? fildyn = 'W.dyn' , >>/ >>EOF >>echo -e "? Calculating Dynamic Matrix...\c" >>$MPIBIN/mpirun -n 6 ph.x -npool 2 <W.ph.in >W.ph.out >>echo -e " DONE" >> >> >> >>-- >>GAO Zhe >>CMC Lab, MSE, SNU, Seoul, S.Korea >> >> >> >>_______________________________________________ >>Pw_forum mailing list >>Pw_forum at pwscf.org >>http://www.democritos.it/mailman/listinfo/pw_forum >> >> >> > > >_______________________________________________ >Pw_forum mailing list >Pw_forum at pwscf.org >http://www.democritos.it/mailman/listinfo/pw_forum > > > _______________________________________________ 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/20110721/a75fcfeb/attachment.htm
