[Pw_forum] Negative frequencies in proximity to the Gamma point problem

[Bahadır SALMANKURT]

Dear Mohammad,

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.

Bests

2017-07-22 11:23 GMT+03:00 Mohammad Alidoosti <m.alidoosti at gmail.com>:

>
> Dear PWSCF users,
>
> 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?
> Hear is the scf input file :
> *********************************************************************
>  &control
>   title = GO
>    calculation = 'scf'
>     restart_mode = 'from_scratch'
>     prefix = 'GO-ph'
>     pseudo_dir = '/home/pseudo'
>     outdir = './tmp/'
>                       nstep  = 200 ,
>                    tstress = .true. ,
>                      tprnfor = .true. ,
>                     verbosity='high',
>                       forc_conv_thr= 1.0d-6
>  /
>  &system
>     ibrav = 0
>     nat = 12
>     ntyp = 3
>     ecutwfc = 80
>     ecutrho = 400
>     occupations = 'smearing'
>     smearing='methfessel-paxton',
>     degauss = 0.001
> /
>  &electrons
> conv_thr= 1.0d-8
> mixing_beta = 0.7
>  electron_maxstep = 200,
>  /
>  &IONS
> /
> &CELL
> cell_dofree = '2Dxy',
> /
> ATOMIC_SPECIES
>   C   12.0107    C.pbe-n-kjpaw_psl.0.1.UPF
>   O   15.999  O.pbe-n-kjpaw_psl.0.1.UPF
>   H   1.008   H.pbe-kjpaw_psl.0.1.UPF
> CELL_PARAMETERS (angstrom)
>    4.990235060   0.054948389   0.000000000
>   -2.541880421   4.219875071   0.000000000
>    0.000000000   0.000000000  25.000000000
>
> ATOMIC_POSITIONS (angstrom)
> O       -0.021826634   0.250928937   1.721705471
> H        0.809321037   0.681392784   1.997855886
> O       -0.031523808   1.135550155  -1.892027240
> H        0.808877574   0.723408478  -2.168118129
> C        0.047350145   0.017290716   0.288486347
> C        0.032454255   1.370630042  -0.458840404
> C       -1.237500438   2.119007372  -0.142173618
> C       -1.224236423   3.485316018  -0.033121650
> C        1.242549808   3.515955831  -0.028144886
> C        1.285890831   2.150271662  -0.137183942
> C        2.528922921   1.430926894  -0.090219298
> C        2.544546281   0.011979550  -0.080086702
> K_POINTS automatic
> 15 15 1 0  0  0
> *******************************************************************
>
> Thanks in advance.
>
> Mohammad Alidoosti
> --
> Institute for Research in Fundamental Sciences (IPM)
> School of Nano-Science
> Shahid Farbin Alley
> Shahid Lavasani st
> P.Code: 19538-33511
> Tehran, Iran
> Tel: +98 21 2310 -3070 <+98%2021%202310%203070>
>
>
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-- 

Bahadır SALMANKURT
---
Ph.D. Candidate
Department of Physics, Sakarya University, TURKEY
---
Research Assistant
Technology Faculty, Department of Information Systems Engineering, Kocaeli
University, TURKEY
Phone : +90 262 303 2208 <+90%20262%20303%2022%2008>
Fax : +90 262 303 2203 <+90%20262%20303%2022%2003>
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