The ABINIT Users Mailing List ( CLOSED )

[Michel Côté <michel.cote@umontreal.ca>]

Title: Re: [abinit-forum] Convergence checking on tsmear + tphysel

I guest I should let Matthieu or Xavier answer but I will give tell you what I understand. Your second statement is correct, by varying the kpt mesh and tsmear we are looking for stability. This is really an integration over k-space and it can be quite difficult to get an accurate integration near the Fermi surface. By giving a finite temperature to your electrons, it smears the Fermi surface which makes the integral easier and less susceptible to charge slushing, i.e. oscillation in the total energy. In general, close to convergence, for a given kpoint grid, the higher the temperature, the lower the free energy (this is what Abinit reports, I think) because of the entropy term: F=E-TS.

Michel

PS: While I was writing, Nicola also answered this question!  


Le 30/03/07 11:19, « jzwanzig@dal.ca » <jzwanzig@dal.ca> a écrit :

> Dear Colleagues, 
>
> even having read the paper by Verstraete and Gonze I'm a little unclear on the interplay between tsmear, tphysel, and occopt. For example, with occopt = 7 and tphysel = 300 K, should the energy be variational in tsmear? That is, am I to expect monotonic behavior in the energy with increasing (or decreasing) tsmear? I kind of hope not as I don't get that, at least for bulk zinc. Is the idea to increase both the kpt mesh and repeatedly vary tsmear, looking for stability (as opposed to a minimum or a maximum)? thanks for your help,
>
> Joe Zwanziger


-- 
*************************************************************** 
  Michel Cote                          tel: +1 (514) 343-5628     
  Professeur agrégé                   fax: +1 (514) 343-2071               
  Département de physique 
  Université de Montréal 
  C.P. 6128, succ. Centre-ville 
  Montréal (Québec) H3C 3J7          Michel.Cote@umontreal.ca 
  Canada                   www.phys.umontreal.ca/~michel_cote 
***************************************************************