[Pw_forum] Serious problem in total energy calculation ?

[Eun-Cheol Lee]

Dear Paolo,

Thank you for kind explanation.
I didn't know this kind of problem in  norm-conserving
pseudopotential, where sufficient kinetic energy
cutoffs are used and negative charge does not exist.
If the relative difference of total energies is not affected,
this is not serious problem. I will check the situation.

In addition, I am sorry for my html mail. I never expected
that my mail is seen broken.

Eun-Cheol Lee

Kyungwon Univ., Korea


----- Original Message ----- 
From: "Paolo Giannozzi" <giannozz at nest.sns.it>
To: <pw_forum at pwscf.org>
Sent: Thursday, June 14, 2007 12:56 AM
Subject: Re: [Pw_forum] Serious problem in total energy calculation ?



On Jun 12, 2007, at 17:09 , ÀÌÀºÃ¶ wrote:

> Thus, the total energy is -31.53657705 Ry, different from the  result of 
> Vanderbilt's code, -31.58339463984 Ry.

reproducing atomic results (typically obtained using real-space
radial grids) with plane waves is tricky: you have to really push
the convergence of the PW calculation. In your example, the PW
energy seems to converge to E=-31.5525 or so (ecutwfc=70,
ecutrho=280). I don't know where the remaining 0.03 Ry difference
may come from, but the usual suspect is the presence of a small
amount of negative charge. Different codes may follow different
recipes on how to deal in that case with the exchange-correlation
potential and energy, and this might well explain the difference in
total energy.

Please post simple text, not html.

Paolo
---
Paolo Giannozzi, Democritos and University of Udine, Italy


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