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Dear Professor Marzari,
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<div class="">I tried tr2_ph=10^-16 for the three q-points I reported earlier and now the two sets give almost identical results. I do get -1.661923 cm^-1 for alpha_mix(1)=0.7 and -1.465509 cm^-1 for alpha_mix(1)=0.3 for the three acoustic modes at the zone
center but I guess that is reasonable and requires ASR treatment. All the other modes are consistent between the two sets.</div>
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<div class="">Thank you for your help.</div>
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<div class="">Vahid</div>
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<div class="">On Jan 13, 2017, at 10:37 AM, Marzari Nicola <<a href="mailto:nicola.marzari@epfl.ch" class="">nicola.marzari@epfl.ch</a>> wrote:</div>
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<div class="">Try tr2A_ph 10^-14, or -16, and report!</div>
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<div class="">Thanks<br class="">
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Sent from a tiny keyboard... Contact info:
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On 13 Jan 2017, at 15:35, Vahid Askarpour <<a href="mailto:vh261281@dal.ca" class="">vh261281@dal.ca</a>> wrote:<br class="">
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Dear QE Community,</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">I have compiled qe-6.0 with intel-14 and openmpi-1.6.5. In attempting to speed up the phonon calculation (as suggested in other posts), I have tried two different alpha_mix(1) values-
the default value of 0.7 and 0.3. For Si, the two alpha_mix values give almost identical phonon frequencies for all q-points. For GaAs, I get different frequencies. I suspect it may be due to the LO-TO splitting at the zone center but the differences exist
for other q-points as well particularly for the acoustic modes. </div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">For example, for q=(0,0,0), I get the following frequencies in wavenumber in the .dyn files:</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">alpha_mix(1)=0.7 : 5.936331, 5.936331, 5.936331, 249.858731,249.858731,249.858731</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">alpha_mix(1)=0.3 : -17.197390, -17.197390,-17.197390, 247.538697, 247.538697, 247.538697</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">For q=(0.125,-0.125,0.125) I get:</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">alpha_mix(1)=0.7 : 31.681603, 31.681603, 62.388768, 246.723626, 246.723626, 266.652186</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">alpha_mix(1)=0.3 : 34.440636, 34.440636, 62.925154, 247.034644, 247.034644, 266.813369</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">For q=(-0.25,0.25,-0.25) I get:</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">alpha_mix(1)=0.7 : 49.997159, 49.997159, 120.235286, 242.448112, 242.448112, 255.746902</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">alpha_mix(1)=0.3 : 52.457875, 52.457875, 121.042662, 242.645430, 242.645430, 255.836026</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">The issue of negative phonon frequencies has been exhaustively discussed on the forum and is not the point of my post. I assume that alpha_mix is not a convergence parameter and should
not change the frequencies but it does. I have also run on SnSe where I do not get negative frequencies at all for either alpha_mix values but the frequencies differ by 10-20 wavenumbers between the two sets. I should add that all self-consistent calculations
for the individual modes reached convergence. Convergence tests were done for the cutoff energy and K-grid as well.</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Here are my input files for the initial self-consistent run followed by the phonon calculation:</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">============================</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> &control</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> calculation = 'scf'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> prefix = 'gaas'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> restart_mode = 'from_scratch'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> wf_collect = .false.</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> pseudo_dir = './'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> outdir = './'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> verbosity = 'high'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> tprnfor = .true.</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> tstress = .true.</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> /</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> &system</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> ibrav=2,celldm(1)=10.838928,</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> nat= 2, ntyp= 2 , nbnd=16</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> ecutwfc = 70, ecutrho=280,</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> occupations = 'fixed'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> /</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> &electrons</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> diagonalization = 'david'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> mixing_beta = 0.7</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> conv_thr = 1.0d-10</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> /</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">ATOMIC_SPECIES </div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Ga 69.723 Ga.pbe-hgh.UPF</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">As 74.92160 As.pbe-hgh.UPF</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">ATOMIC_POSITIONS crystal</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> Ga 0.0 0.0 0.0</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> As -0.25 0.75 -0.25</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">K_POINTS automatic</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> 12 12 12 0 0 0</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">==============================</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">GaAs</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">&inputph</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> tr2_ph = 1.0d-12</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> prefix = 'gaas'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> amass(1) = 69.723</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> amass(2) = 74.92160</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> ldisp = .true.</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> epsil = .true.</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> nq1=8, nq2=8, nq3=8</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> outdir = './'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> alpha_mix(1)=0.3</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> fildyn = 'gaas.dyn'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> fildvscf = 'dvscf'</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class=""> /</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">I would appreciate any input as to why alpha_mix alters the results for polar materials such as GaAs and SnSe.</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Thank you,</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Vahid</div>
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<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Vahid Askarpour</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Department of Physics and Atmospheric Science</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Dalhousie University,</div>
<div style="margin: 0px; font-size: 12px; line-height: normal;" class="">Halifax, NS, Canada</div>
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