[Pw_forum] Relaxation of Cu100 with PBE pseudopotential

[Alcantara Ortigoza, Marisol]

Dear Andrea,

Thanks for replying. It's worth to try those values , however the same
value for broadening was used in both calculations and the volume of the
two systems was almost the same (differing by just 0.9%), then the
Brilloruin zone differed by 0.9% too. The k-point sampling density,
therefore, should be same for both systems. Thus, if the broadening were
a problem for the first calculation, it should also be a problem for the
second one, but for the second calculation I got the correct result
according to the experiment.

Best regard.

Marisol.

-----Original Message-----
From: pw_forum-admin at pwscf.org [mailto:pw_forum-admin at pwscf.org] On
Behalf Of Andrea Ferretti
Sent: Friday, February 11, 2005 11:36 AM
To: PWSCF forum list
Subject: RE: [Pw_forum] Relaxation of Cu100 with PBE pseudopotential



dear Marisol,

addressing the point of nicola, the convergence the convergence of kpt
mesh should be carefully checked when dealing with metals.... here a
broadening of 0.05 Ry = 0.68 eV (!!) seems to me to be too large,
probably missing the detailed structure of energy bands and the position
of the Fermi level for instance.... which results in unconverged
physical properties..... the broadening value should be chosen in
accordance with the choice of the kpt mesh, and, to my (limited)
experience, some "reasonable" values are between 0.004 and 0.01 Ry...

I don't know if this may explain the disagreement and oscillation in
results you observed but the broadening you set looks quite
'unusual'.... hope it helps Andrea

-- 
Andrea Ferretti
INFM National Research Center on nanoStructures and bioSystems at
Surfaces (S3) Dipartimento di Fisica, Universita' di Modena e Reggio
Emilia Via Campi 213/A I-41100 Modena, Italy
Tel:     +39 059 2055283
Fax:     +39 059 367488
E-mail:  ferretti.andrea at unimore.it
URL:     http://www.nanoscience.unimo.it

On Fri, 11 Feb 2005, Alcantara Ortigoza, Marisol wrote:

> Hi,
>
> Thank you very much for replying.
>
> I did not change anything in the input file for each case, but the 
> lattice constant. So, in both cases the k-point sampling was 9X9X1. 
> This mesh gave us 15 special kpoints, while the temperature broadening

> was 0.05 ryd.
>
> 1) For a = 3.67 A
>
> Fermi energy = 5.3079 ev
>
> Highest band energy = 10.9354 ev
>
> # bands above the Fermi energy : 17
>
> 2) For a = 3.6737 A
>
> Fermi energy =   5.5509 ev
>
> Highest band energy = 11.2380 ev
>
> # bands above the Fermi energy : 17
>
> Thank you very much.
>
> Marisol Alcantara Ortigoza.
>
>
>
> -----Original Message-----
> From: pw_forum-admin at pwscf.org [mailto:pw_forum-admin at pwscf.org] On 
> Behalf Of Nicola Marzari
> Sent: Thursday, February 10, 2005 7:03 PM
> To: pw_forum at pwscf.org
> Subject: Re: [Pw_forum] Relaxation of Cu100 with PBE pseudopotential
>
>
>
>
> In these calculations it is essential to have an
> accurate k-point sampling and some finite temperature broadening.
>
> What were you using in both cases ? How many bands did you have above 
> the Fermi energy ?
>
> 			nicola
>
>
> Alcantara Ortigoza, Marisol wrote:
>
> > Hi,
> >
> > I was trying to relax Cu100 using 9 p(2x2) layers + 9 vacuum by 
> > using PBE pseudopotential provided by pwscf.
> >
> ---------------------------------------------------------------------
> Prof Nicola Marzari   Department of Materials Science and Engineering
> 13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
> tel 617.4522758  fax 617.2586534  marzari at mit.edu  http://nnn.mit.edu 
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