[Pw_forum] Bilayer graphene with an electric field applied

[Elie Moujaes]

Thanks very much for your help. I will use the sawtooth potential and see what happens. I will have another look on the band structure as well because I have done the DOS calculations and the graph seems pretty ok..

 

Regards

 

Elie
 


Date: Wed, 29 Sep 2010 09:55:03 +0200
From: sclauzer at sissa.it
To: pw_forum at pwscf.org
Subject: Re: [Pw_forum] Bilayer graphene with an electric field applied


Dear Elje,

   since you are dealing with a slab geometry and you want to apply the field along the direction perpendicular to the surface, why don't you use the sawtooth potential (tefield=.TRUE. instead of lefield=.TRUE.) to generate the E field?

On 09/28/2010 10:41 PM, Elie Moujaes wrote: 


Dear all,
I
I am trying to get the band structure of graphene under the effect of an electric field. The problem is that the result at the end is very messy and jiggly. I repeated the calculations many times but I still get the same result. I first performed a scf calculation without the electric field followed by a scf calculation with an electric field and then the band calculation.
    

Do you have some evidence that your "messy and jiggly" band structure is wrong? Are you sure that you are visualizing it in the correct way?


HTH


GS


 
SCF with electric field
 

&control
    prefix='bi elgraphene',
    calculation='scf',
    restart_mode='from_scratch',
    lelfield = .true.,
    pseudo_dir = '/espresso-4.2/pseudo/',
    outdir='/tmp/results_MOUJAES/'
 /
  &system    
    ibrav=  4, celldm(1) =4.608737, celldm(3)=5.330410, nat=4, ntyp= 1,
    ecutwfc = 110.D0,occupations='smearing',smearing='methfessel-paxton', degauss=0.01
/
 &electrons
    conv_thr=1.D-10,     
    mixing_mode='plain'
    efield_cart(1) = 0.0,
    efield_cart(2) = 0.0,
    efield_cart(3) = 0.001,
    startingwfc = 'random'
 
 /
ATOMIC_SPECIES
 C  12.0107  C.pz-vbc.UPF
ATOMIC_POSITIONS crystal
 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
   38 38 1  0 0 0   
I noticed that part of the bands calculation output had a problem with the convergence of one of thh eigenavalues as some of the input looked like:
 

per-process dynamical memory:    30.2 Mb

     Band Structure Calculation
     Davidson diagonalization with overlap
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged
     c_bands:  1 eigenvalues not converged

 
Please can anyone suggest me of what could have gone wrong...
 
Thanks
 
Elie Moujaes
University of Nottingham
NG7 2RD
UK
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-- 

Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne

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