[Pw_forum] query on fermi energy
On Jan 16, 2012, at 19:06 , Ajit Vallabhaneni wrote: > Sorry i didnot understand your question. I don' understand why you insist that something is not working and don't provide any evidence. --- Paolo Giannozzi, Dept of Chemistry, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
[Pw_forum] query on fermi energy
Dr.Paolo, Sorry i didnot understand your question. Thanks Ajit
[Pw_forum] query on fermi energy
On Jan 15, 2012, at 12:50 , Ajit Vallabhaneni wrote: > I observed that using a dense grid is not enough sometimes you observed in which case? P. --- Paolo Giannozzi, IOM-Democritos and University of Udine, Italy "Nothing is impossible for the man who doesn't have to do it himself"
[Pw_forum] query on fermi energy
Dr. Paolo, Like in graphene, i used 60x60 mesh, but for some q-points it terminates with the message that "it is not a part of dense grid". Should i increase the grid size even more? It is very expensive computationally though. Thanks Ajit
[Pw_forum] query on fermi energy
Dear Peter, also, there is an example in the qe distribution on how to calculate fermi energies via slab calculations - and there is extensive literature - e.g. the PhD thesis of Caspar Fall http://library.epfl.ch/en/theses/?nr=1955 , or Phys. Rev. B 80, 235407 (2009). nicola On 1/14/12 6:14 PM, Peter Wang wrote: > if we do a bulk calculation, vacuum energy level can not be calculated, > because in bulk, there is no vacuum. To calculate vacuum energy level and > the relative energies in bulk with respect to vacuum energy level, a slab > calculation should be done. In a slab calculation, several layer of > materials as well as a vacuum with sufficient thinkness should be included > in one unit cell. > > YP > > -- > From: Ajit Vallabhaneni > Sent: Sunday, January 15, 2012 1:06 AM > To: PWSCF Forum > Subject: Re: [Pw_forum] query on fermi energy > > Yun-peng, > > Thanks for your response. Is it possible to know what the vaccum > energy level is ? I read in the FAQ that it cannot be calculated from the a > bulk calculation alone. > > > Thanks > Ajit > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum -- -- Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
[Pw_forum] query on fermi energy
Any thoughts on my second question regarding the e-ph calculation. For a give set of q and k points, what is the best way to ensure that all k+q points are available to avoid the message " q is not a vector in the dense grid" in the calculations"? I observed that using a dense grid is not enough sometimes. Do we have to check it outside of the quantum espresso before the calculation begins? Thanks Ajit
[Pw_forum] query on fermi energy
if we do a bulk calculation, vacuum energy level can not be calculated, because in bulk, there is no vacuum. To calculate vacuum energy level and the relative energies in bulk with respect to vacuum energy level, a slab calculation should be done. In a slab calculation, several layer of materials as well as a vacuum with sufficient thinkness should be included in one unit cell. YP -- From: Ajit Vallabhaneni Sent: Sunday, January 15, 2012 1:06 AM To: PWSCF Forum Subject: Re: [Pw_forum] query on fermi energy Yun-peng, Thanks for your response. Is it possible to know what the vaccum energy level is ? I read in the FAQ that it cannot be calculated from the a bulk calculation alone. Thanks Ajit ___ Pw_forum mailing list Pw_forum at pwscf.org http://www.democritos.it/mailman/listinfo/pw_forum
[Pw_forum] query on fermi energy
for the first question, there is no absolute Fermi energy. The only absolute energy is that substracting vacuum energy level from it. best Yun-Peng -- From: Ajit Vallabhaneni Sent: Saturday, January 14, 2012 3:32 PM To: PWSCF Forum Subject: [Pw_forum] query on fermi energy Dear users, 1. I was wondering how to calculate the absolute value of fermi energy for graphene single layer. By varying the size of the super cell in the out of plane direction, i observed that the total energy is constant indicating no interactions in the out of plane direction, but the fermi energy is varying with increasing distance. I think it is the relative fermi energy which is output after the scf calculation. I want to know the absolute value. 2. Another question i have is regarding the e-ph calculation. For a give set of q and k points, what is the best way to ensure that all k+q points are available to avoid the message " q is not a vector in the dense grid" in the calculations"? I observed that using a dense grid is not enough sometimes. Do we have to check it outside of the quantum espresso before the calculation begins? Thanks Ajit ___ Pw_forum mailing list Pw_forum at pwscf.org http://www.democritos.it/mailman/listinfo/pw_forum
[Pw_forum] query on fermi energy
Dear users, 1. I was wondering how to calculate the absolute value of fermi energy for graphene single layer. By varying the size of the super cell in the out of plane direction, i observed that the total energy is constant indicating no interactions in the out of plane direction, but the fermi energy is varying with increasing distance. I think it is the relative fermi energy which is output after the scf calculation. I want to know the absolute value. 2. Another question i have is regarding the e-ph calculation. For a give set of q and k points, what is the best way to ensure that all k+q points are available to avoid the message " q is not a vector in the dense grid" in the calculations"? I observed that using a dense grid is not enough sometimes. Do we have to check it outside of the quantum espresso before the calculation begins? Thanks Ajit
