EPW Forum

[img]Dear all,

Presently, I am checking the differences in phonon dispersions in EPW before and after Wannier interpolation. Surprisingly, the frequencies are differ by 2-5cm-1 between two methods and the behavior of dispersion (specifically, along G-M acoustic phonons and at K-high symmetry point in attached images) is quite wired. I also checked with the spreads, which are less than 2angstrom as shown in below.

Wannier Function centers (cartesian, alat) and spreads (ang):
( -0.00183 0.00047 3.48371) : 1.82145
( -0.00672 0.00042 3.48371) : 1.98119
( 0.00663 -0.00032 3.48371) : 1.97895
( 0.04603 0.00032 3.48371) : 1.92290
( -0.04293 -0.00104 3.48371) : 1.92244
( 0.17439 0.51667 4.03591) : 1.22353
( 0.24157 0.50747 3.79261) : 1.34094
( 0.41964 0.50332 3.97007) : 1.20749
( 0.26905 0.38659 3.93307) : 1.53420
( 0.17439 0.51667 2.93151) : 1.22353
( 0.24157 0.50747 3.17482) : 1.34094
( 0.41964 0.50332 2.99736) : 1.20749
( 0.26905 0.38659 3.03436) : 1.53420

I also run with high q-grids (16X16X1) for phonon dispersions and my EPW.in is as below

fsthick = 4.0 ! eV
eptemp = 300 ! K (same as PRB 76, 165108)
degaussw = 1.0 ! eV
degaussq = 0.05 ! meV
dvscf_dir = '/scratch/03972/konda16/M/S/mono/Gauss-0.18/save/'
filukk = './MS2.ukk'
nkf1 = 64
nkf2 = 64
nkf3 = 1
nqf1 = 64
nqf2 = 64
nqf3 = 1
nk1 = 16
nk2 = 16
nk3 = 1
nq1 = 16

nq2 = 16
nq3 = 1

Kindly suggest me the error bar for the same. Also, I am curious to know about the differences between degaussw (in epw.in) and degauss in phonon calculations. Shall use same parameters for both calculations???

PS: How attach figures along with our doubts!!!

Thanks in advance
with regards
S.Appalakondaiah

Dear S.Appalakondaiah,

You can upload your figure on an image free website and post the link here.

So what you are saying is that the result for the phonon bandstructure is different if you use EPW and if you use matdyn.x ?

Are you using the 'simple' acoustic sum rule?

The way the asr is imposed in EPW is different from matdyn. In matdyn the asr is imposed in real space and in EPW in reciprocal space.

This can lead to difference (especially for 2D materials).

Carla implemented the possibility to impose the ASR in real space to reproduce the same results as matdyn (also using different sum rule).
This will be release in the next version of EPW (version 4.2).

Best,

Samuel

Dear Dr. Samuel,

Thank you very much for quick reply. I used asr as crystal in the matdyn.in and hope this might be the reason.

I am also looking for the differences in degaussw in EPW and degauss in PWSCF-scf inputs. For example I am using 0.2 eV (~0.02 Ry)degauss in PWSCF and 1.0 eV in EPW calculations. The obtained lambda and Tc are very well with experiments. But I want to confirm the result be accidentally happen or 1 eV of degaussw is best for my system!!!. Can you please provide me any references for choosing degaussw in EPW!!

Thanks in advance

with regards
S. Appalakondaiah