[Pw_forum] Bilayer graphene subject to an electric field

Elie Moujaes elie.moujaes at hotmail.co.uk
Fri Dec 17 16:47:51 CET 2010

Dear Prof. Eyvaz,
Thanks a lot for the information. Everything is solved now..

Date: Tue, 14 Dec 2010 13:40:59 -0800
From: eyvaz_isaev at yahoo.com
To: pw_forum at pwscf.org
Subject: Re: [Pw_forum] Bilayer graphene subject to an electric field


A  couple of comments that might be useful.

1. As you use an US pseudopotential, reduce ecutwfc down to ~30Ry. I do not see any reason for such kind of high cutoff energy, unless you performed some tests and proved that 60Ry is better. Besides, for the same reason (US PsP), you should use more ecutrho (8-12 times of  ecutwfc). By default ecutrho=4*ecutwfc (why so, think about) and this works for norm-conserving PsPs. 

As a reference see  N.Mounet and N. Marzari, Phys. Rev. B 71, 205214 (2005), where they used ecutoff=40Ry for graphene and other C-based structures.

2. I have noticed that the job started to converge when I used smaller efield_cart(3)=0.05,  after 49  iteration  I had

     estimated scf accuracy    <       0.00007068 Ry

but then my notebook turned off due to a heating problem, I suggest. As I just tried to test the problem I used only 2x2x1 k-points set, and mixing_beta(1)=0.05. 
But when I used   efield_cart(3)=0.005 (with mixing coefficient  0.1) the job finished after 11 iterations. 

Hope this helps.

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: Elie Moujaes <elie.moujaes at hotmail.co.uk>
To: pw_forum at pwscf.org
Sent: Mon, December 13, 2010 1:57:36 PM
Subject: [Pw_forum] Bilayer graphene subject to an electric field

Dear all,
I am trying to get the band structure of bilayer graphene under the effect of an external electric field. I have done the scf calculations without the inclusion of an electric field , then again did teh scf calculation with an electric field included in the z-direction (of value 0.1 Ry). However the convergence is not achieved and it stopped after 100 iterations giving the following message:

     total cpu time spent up to now is  83435.11 secs

     total energy              =     -52.83248336 Ry
     Harris-Foulkes estimate   =     -45.80937450 Ry
     estimated scf accuracy    <       0.00524127 Ry

     End of self-consistent calculation

     convergence NOT achieved after 100 iterations: stopping

You will find below the inout file for the scf calculation when an electric field is applied:
    lelfield = .true.,
    nberrycyc= 1,
    pseudo_dir = '/espresso-4.2/pseudo/',
    ibrav=  4, celldm(1) =4.608737, celldm(3)=5.330410, nat=4, ntyp= 1,
    ecutwfc = 60.D0,occupations='smearing',smearing='methfessel-paxton', degauss=0.01
    efield_cart(1) = 0.000,
    efield_cart(2) = 0.000,
    efield_cart(3) = 0.10,
 C  12.0107  C.pz-rrkjus.UPF
 C 0.000000  0.000000  0.000000  
 C 0.000000  0.000000  0.257692 
 C 0.333333  -0.33333  0.000000  
 C -0.333333  0.33333  0.257692  
K_POINTS automatic
   25 25 1  0 0 0  
Elie Moujaes
University of Nottingham

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