[Pw_forum] why the results obtained from pwscf have so big difference with experiment

[Stefano Baroni]

\Delta V \approx { {\partial E\over \partial V} \over {\partial^2 E  
\over \partial V^2}}

the trace of the stress tensor gives the numerator; the denominator  
can be estimated by finite-difference differentiation
the rest is left as an exercise ...

SB

On Nov 24, 2008, at 9:38 AM, xu yuehua wrote:

> en, in general, the P is somewhat big,(i have a look at  the forum  
> posted before)
> but if i should estimate the change of volume, what is the dV/da (c)  
> criterion?
>
>
> 2008/11/24 Paolo Giannozzi <giannozz at democritos.it>
> xu yuehua wrote:
>
> > why P is so big ?
>
> try to estimate how much the volume should change in order to
> offset the pressure, before claiming that "P is big"
>
> Paolo
> --
> Paolo Giannozzi, Democritos and University of Udine, Italy
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>
>
> -- 
> Xu Yuehua
> physics Department of Nanjing university
> China
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Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
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