[Pw_forum] about ecutwfc convergence for total energy

[James Mao]

Thanks Carlo. The system is not metallic. Just as I mentioned, only atom
types it 
includes are H, C, N, O, S, P, F.

I noticed last month Peng reported a similar observation:
http://www.democritos.it/pipermail/pw_forum/2012-September/025080.html

In his case he used smearing, and kpoints(4,4,3). His PP is also NC pbe
(pbe-n-kjpaw), 
and observed a minimum at ecut=80, very similar to my case. 

Best,
James

-----Original Message-----
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
Behalf Of Carlo Nervi
Sent: Tuesday, October 09, 2012 3:07 AM
To: pw_forum at pwscf.org
Subject: Re: [Pw_forum] about ecutwfc convergence for total energy

Hi,
as far as i know it seems a problem related with bands, so low number of
k-points (for insulators).
I would suggest in any cases to try to use a couple of k-points.
Another important point: are you sure your system is not metallic?
In this case you could try smearing.
HTH,
	Carlo

Il 08/10/2012 17.05, James Mao ha scritto:
> Hi all,
>
> I am a little bit confused about ecutwfc convergence. I am working on 
> calculating NMR of a crystal structure. Before that I need test SCF 
> energy convergence.
> However I noticed the total energy is not convergent with respect to 
> ecutwfc.
>
> It reached minimum at ecutwfc=90 then began oscillating up and down.
>
> Ecutwfc  Total Energy
>
> 70           -3249.733804
>
> 80           -3250.674250
>
> 90           -3250.827326
>
> 100         -3250.661301
>
> 120         -3250.346091
>
> 160         -3250.582989
>
> 200         -3250.395401
>
> I think higher ecutwfc means more basis functions, therefore should 
> always result in a lower total energy. If I am wrong, should I keep 
> increasing ecutwfc?
>
> The PP I used is (pbe-tm-new-gipaw-dc.UPF), the atoms include C, O, N, 
> F, S, H, P.
>
> Since PP is NC, I left ecutrho default. And since the cell is pretty 
> big (a~10, b~16, C~15), I only calculated at gamma point.
>
> Any hint is helpful! Thanks.
>
> Best,
>
> James Mao
>
> ----------------------------------
>
> Postdoc, Department of Chemistry, University of Pittsburgh
>
>
>
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--
------------------------------------------------------------
Prof. Carlo Nervi carlo.nervi at unito.it  Tel:+39 0116707507/8
Fax: +39 0116707855      -      Dipartimento di Chimica, via
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