[Pw_forum] Plotting graphene band

[Yusuf Zuntu]

Dear All
Can some please help me suggest the range of energy and delta E for extracting band data for graphene in its primitive cell (only two carbon atoms). I have tried several ranges with fermi level set
at zero but still the band plotted with QE plotting band option looks very unusual.


________________________________
 From: Eduardo Ariel Menendez Proupin <eariel99 at gmail.com>
To: pw_forum at pwscf.org 
Sent: Wednesday, September 26, 2012 8:44 PM
Subject: Re: [Pw_forum] ecutwfc convergence
 

Dear Yusuf 
The cutoff depends on the pseudopotential that you use, not just on the atom. Different pseudopotentials for the same atoms have different cutoff. Also, some properties requiere higher cutoffs than others. For example, forces and relative energies need lower cutoff than total energy and stress. Using higher values does not harm, just take longer time and more computer resources.  Some programs include recommended cutoffs in the pseudopotential, but the user is still responsible of testing it. 

If you want a starting parameter for graphene, use 
C.pz-vbc.UPF with ecutwfc = 60.0 , 
or 
C.pbe-rrkjus.UPF with ecutwfc = 30.0 and ecutrho = 180.0
the above work reasonably well to relax the structures with fixed cell, and to get the bands and DOS. I fou want to calculate elastic properties or LDA+U or PBE+U, or calculate conductance, etc, etc, these cutoffs may be too low. Yo need to do tests increasing the values until you see no change in the property that you want to calculate. 
If you plan to adsorb other atoms (e.g. oxygen) on the graphene, then determine cutoffs that are valid for the full system and do all the calculations with the same parameters. 

Dear Manasaje The system is graphene with 32 carbon atoms. The cutoff is not specified in the pseudo and I need it before proceeding to other SCF and nscf calculations and believe, cutoff is a property of an atom in question. So can I still go ahead with the atoms in the unit cell. Thank you for your quick response
Yusuf ________________________________ From: Eduardo Ariel Menendez Proupin <eariel99 at gmail.com>
To: pw_forum at pwscf.org Sent: Wednesday, September 26, 2012 7:18 PM
Subject: Re: [Pw_forum] ecutwfc convergence Dear Yusufm  ecutwfc and ecutrho depend only on the hardest of the pseudopotentials used for the atoms in the molecule or the crystal. If your molecule is C32 and have no other elements, you can make tests with a C2 (which does not exists, I guess), and the cutoffs for C32.  Anyway, if your are going to calculate something that it is not the total energy or the DOS, let's say, the phonons, or the Raman spectrum, it is reasonable that you test the effect of the cutoff first on C2 and then on C32. 
---------- Mensaje reenviado ----------
From: Yusuf Zuntu <yzunt at yahoo.com>
To: PWSCF Forum <pw_forum at pwscf.org>
Cc: 
Date: Wed, 26 Sep 2012 03:15:32 -0700 (PDT)
Subject: [Pw_forum] ecutwfc convergence Hi,
I need clarification on kinetic energy cutoff. I have a system comprising 32 carbon atoms. Am I to consider total 32 carbon atoms in  convergence w.r.t kinetic energy cutoff scf calculation or the two carbon atoms in the unit cell.
Thank you for anticipated reply.
Yusuf-- 


Eduardo Menendez Proupin
Departamento de Química Fisica Aplicada
Facultad de Ciencias
Universidad Autónoma de Madrid
28049 Madrid, Spain

Phone: +34 91 497 6706

On leave from: Departamento de Fisica, Facultad de Ciencias, Universidad de Chile URL: http://fisica.ciencias.uchile.cl/%7Eemenendez

"Padece, espera y trabaja para gentes que nunca conocerá y que a su vez padecerán, esperarán y trabajarán para otros, que tampoco serán felices, pues el hombre ansía siempre una felicidad situada más allá de la porción que le es otorgada. Pero la grandeza del hombre está precisamente en querer mejorar lo que es. En imponerse Tareas. En el Reino de los Cielos no hay grandeza que conquistar, puesto que allá todo es jerarquía establecida, incógnita despejada, existir sin término, imposibilidad de sacrificio, reposo y deleite. Por ello, agobiado de penas y de Tareas, hermoso dentro de su miseria, capaz de amar en medio de las plagas, el hombre puede hallar su grandeza, su máxima medida en el Reino de este Mundo".
Alejo Carpentier, El reino de este mundo, (1949).

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and works for peoples he will never meet, and who at the same time will 
suffer and wait and work for others who will also not be happy, as man 
always desires a happiness that is beyond the lot that he is given. But 
the greatness of man is precisely in wanting to improve what he is. In 
assigning himself Tasks. In the Kingdom of Heaven there is no greatness 
to conquer, for everything there is an established hierarchy, the 
unknown is unobscured, existence is without end, sacrifice, rest, and 
delight are impossibilities. Therefore, overwhelmed with hardships and 
Tasks, beautiful within his misery, capable of loving in the middle of 
calamity, man can only find his greatness, his full self-realization, in the Kingdom of this World." - Alejo Carpentier


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