[Pw_forum] finite displacement phonon calculation
Merlin Meheut
merlin.meheut at gmail.com
Wed May 25 18:43:04 CEST 2016
Dear PWSCF users,
The following message might have been lost, so I permit myself to reiterate
it: would someone have an idea why the finite displacement method as
implemented in quantum espresso v 5.1. gives wrong matrices of interatomic
force constants when supercell options are taken?
Also, I was wondering if an example of input would be available for using
fd_ef.x (calculation of dielectric constants and effective charges by
finite displacement).
Thanks in advance for any help,
Best regards,
Merlin Méheut, PhD,
Géosciences et Environnement Toulouse, OMP,
Université Paul Sabatier Toulouse III,
14 avenue Edouard Belin, 31400 Toulouse, France
phone +33 (0)5 61 33 26 17, fax +33 (0)5 61 33 25 60
https://www.researchgate.net/profile/Merlin_Meheut
2016-04-26 16:54 GMT+01:00 Merlin Meheut <merlin.meheut at gmail.com>:
> Dear QE users and developpers,
>
> I would like to compute phonon properties using the finite displacement
> method, as proposed in the example of quantum espresso version 5.1
> (PHonon/FD/example). For frequencies at q=0, the answer is reasonably close
> to the results of DFPT, but for q-vectors different from zero, I find very
> negative frequencies, and very different from DFPT.
>
> Follows a description of my calculations. Any help would be thoroughly
> appreciated.
>
> My system is forsterite Mg2SiO4 (orthorhombic Pbnm):
>
> &system
> ibrav =0, celldm(1)=8.985459,
> nat =28, ntyp = 3, ecutwfc =${a}.0, ecutrho = ${b}.0
> /&end
>
> CELL_PARAMETERS (alat= 8.98545900)
> 1.011800931 0.000000000 0.000000000
> 0.000000000 2.175636534 0.000000000
> 0.000000000 0.000000000 1.273688789
>
> ATOMIC_POSITIONS (crystal)
> Mg -0.000000000 -0.000000000 -0.000000000
> Mg 0.500000000 0.500000000 -0.000000000
> Mg -0.000000000 0.000000000 0.500000000
> Mg 0.500000000 0.500000000 0.500000000
> Mg 0.991704573 0.277641327 0.250000000
> Mg 0.491704573 0.222358673 0.750000000
> Mg 0.008295427 0.722358673 0.750000000
> Mg 0.508295427 0.777641327 0.250000000
> Si 0.425939676 0.093656753 0.250000000
> Si 0.925939676 0.406343247 0.750000000
> Si 0.574060324 0.906343247 0.750000000
> Si 0.074060324 0.593656753 0.250000000
> O 0.765422396 0.091530172 0.250000000
> O 0.265422396 0.408469828 0.750000000
> O 0.234577604 0.908469828 0.750000000
> O 0.734577604 0.591530172 0.250000000
> O 0.222541031 0.447081956 0.250000000
> O 0.722541031 0.052918044 0.750000000
> O 0.777458969 0.552918044 0.750000000
> O 0.277458969 0.947081956 0.250000000
> O 0.277386450 0.162817013 0.033263088
> O 0.777386450 0.337182987 0.966736912
> O 0.722613550 0.837182987 0.533263088
> O 0.222613550 0.662817013 0.466736912
> O 0.722613550 0.837182987 0.966736912
> O 0.222613550 0.662817013 0.033263088
> O 0.277386450 0.162817013 0.466736912
> O 0.777386450 0.337182987 0.533263088
>
> On one had I have made a phonon (perturbation theory) calculation on a
> 2x2x2 grid of the Brillouin zone, deliberately without Born charges and
> dielectric tensor (since I do not do it with finite displacements):
>
> &inputph
> amass(1)=23.9850,
> amass(2)=27.9769,
> amass(3)=15.9949,
> alpha_mix(1) = 0.7,
> ldisp=.true., nq1=2, nq2=2, nq3=2,
> tr2_ph = 1.0D-16,
> prefix='FOR',
> fildyn='mat.$PREFIX',
> lraman=.false.,
> epsil =.false.,
> trans =.true.,
> zue = .false.,
> outdir='*/tmpdir/*$LOGNAME/'
> /&end
> 0.0 0.0 0.0
>
> Then I obtained an ifc matrix with q2r and re-calculated the frequencies
> with matdyn on the 8 q-points (finding the same frequencies as directly
> from the individual dynamical matrices).
> For example, for q= (0.5,0,0) I find the following frequencies:
>
> 152.7355 152.7355 159.2373 159.2373 159.6323 159.6323
> 171.3805 171.3805 177.2753 177.2753 191.6439 191.6439
> 202.0364 202.0364 244.3864 244.3864 244.9694 244.9694
> 264.4823 264.4823 277.6309 277.6309 279.3910 279.3910
> 287.4779 287.4779 288.9345 288.9345 295.9524 295.9524
> 307.4176 307.4176 309.7795 309.7795 329.0229 329.0229
> 332.7833 332.7833 339.4032 339.4032 346.7481 346.7481
> 371.5853 371.5853 403.7708 403.7708 423.2761 423.2761
> 436.9743 436.9743 458.7147 458.7147 459.0536 459.0536
> 482.4561 482.4561 493.6059 493.6059 501.4041 501.4041
> 530.9486 530.9486 550.9678 550.9678 560.3782 560.3782
> 603.1617 603.1617 786.0294 786.0294 800.2429 800.2429
> 820.2436 820.2436 842.1800 842.1800 846.5773 846.5773
> 854.6477 854.6477 947.1591 947.1591 992.4286 992.4286
>
> On the other hand, I realized a finite displacement calculation with fd.in
> below:
>
> &inputfd
> fd_prefix = 'FOR'
> fd_outdir = '*/tmpdir/mmeheut/*'
> fd_outfile = 'displaced'
> fd_outfile_dir = './fd_files'
> nrx1 = 2
> nrx2 = 2
> nrx3 = 2
> innx = 1
> de = 0.01
> /
>
> and fd_ifc.in
>
> &input
> prefix='FOR'
> nrx1=2,
> nrx2=2,
> nrx3=2,
> de=0.01,
> file_force='./fd_files/force',
> file_out='./For-rel-pbeUS.80Ryx4-222111.fd222',
> innx=1
> nodispsym=.false.
> noatsym=.false.
> verbose=.true.
> hex=.false.
> /
>
> the ifc matrix I obtain is a bit different from DFPT but it is difficult
> to make clearer statement. When I use matdyn to obtain frequencies, at q=0
> it is correct, but at q= (0.5,0,0) for example, I have:
>
> -549.4798 -549.4798 -542.0251 -542.0251 -270.8103 -270.8103
> -270.3831 -270.3831 -268.2961 -268.2961 -255.8122 -255.8122
> -229.8735 -229.8735 -224.8183 -224.8183 -219.7591 -219.7591
> -205.2850 -205.2850 -200.4448 -200.4448 -197.4146 -197.4146
> 131.2067 131.2067 143.8600 143.8600 155.3084 155.3084
> 163.2342 163.2342 181.7740 181.7740 200.2658 200.2658
> 213.1614 213.1614 243.0599 243.0599 254.4463 254.4463
> 257.8945 257.8945 270.8913 270.8913 271.1355 271.1355
> 277.1344 277.1344 280.2588 280.2588 296.9960 296.9960
> 339.1382 339.1382 344.2783 344.2783 346.3596 346.3596
> 360.5026 360.5026 369.8420 369.8420 387.3814 387.3814
> 457.0229 457.0229 491.8080 491.8080 512.6835 512.6835
> 576.2465 576.2465 588.0433 588.0433 596.5263 596.5263
> 608.6300 608.6300 623.7900 623.7900 628.1992 628.1992
>
> The symetry does seem correct, but the frequencies are completely off..
>
> Thanks again for any help,
>
> Sincerely,
>
> Merlin Méheut
>
> --
> Merlin Méheut, Géosciences et Environnement Toulouse,
> OMP, 14 avenue Edouard Belin, 31400 Toulouse, France
>
> phone +33 (0)5 61 33 26 17, fax +33 (0)5 61 33 25 60
>
>
--
Merlin Méheut
adresse labo:
GET - OMP - Université Paul Sabatier
14 avenue Edouard Belin
31400 Toulouse
FRANCE
tel: (+33) 5 61 33 26 17
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