[Pw_forum] Serious problem in total energy calculation ?

[Paolo Giannozzi]

On Jun 12, 2007, at 17:09 , 이은철 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
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Paolo Giannozzi, Democritos and University of Udine, Italy