[Pw_forum] Etot in cp.x vs pw.x

[Lorenzo Paulatto]

On Sun, Jul 22, 2012 at 10:55 PM, sylvian <sylviankahane at gmail.com> wrote:

> cp.x is printing an Etot at the end of the run (in my case something like
> -47 Ha). Taking its state at the end of the run, i.e. ions positions and
> charge density, as an input to pw.x (admittedly with a different
> pseudopotential)  I am getting a "total energy" differing by an order of
> magnitude (in my case -800 Ry).
>
>
>

Dear Sylvan,
absolute energies have no meaning in general. There can be some more or
less natural choices for a zero energy, but n periodic boundary conditions
and with pseudopotential there is none that really makes sense.

It is also true that with fairly similar pseudopotential you often get
similar (if equally meaningless) "total" energies. You are not specifying
which pp's you're using so I can only guess:
1. the pp used in pw.x has more valence electrons
2. the pp used in pw.x is actually a paw dataset, and you are comparing the
all-electron energy with the valence one

best regards

-- 
Lorenzo Paulatto IdR @ IMPMC/CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
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