[Pw_forum] pressure at 20Gpa

[Ari P Seitsonen]

Dear A Rajkamal,

   Adding to the response of Xi, well, it depends on the material: Indeed 
in most materials the pressure fo 400 GPa - or 20 GPa, like is written 
in the Subject of this email? - is so strong that the atoms are pushed 
very much toward each other and the core regions start to overlap so much 
that the pseudo potential approximation starts to fail.

   Or are you motivated by the recent study of hydrogen under 325 GPa 
(article in 'Nature' this month)? In that case one could create a pseudo 
potential with a very small core radius, basically just to get rid of the 
cusp that requires a higher cut-off energy. Or even using a bit higher 
cut-off energy and the -1/r potential. This procedure is possible in only 
few special elements, so in the general case indeed better go for real 
all-electron methods.

     Greetings,

        apsi

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   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
     Ecole Normale Supérieure (ENS), Département de Chimie, Paris
     Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Mon, 18 Jan 2016, Raj kamal wrote:

> 
> dear QE experts,
> can i use pressure upto 400Gpa in quantum espresso for VC ralaxation. is
> there any limitations using this pressure parameter.
> thanks in advance.
> --
> Best regards,
> Rajkamal.A.
> Research Scholar,(SRM UNIV).
> 
>