# [Pw_forum] Bulk modulus under pressure?

Mon Feb 27 06:58:37 CET 2012

```thanks for  quick,

i just tried a quick calculation for my curiosity on this.  i just
optimized a fcc structure under 100GPa pressure also under 0GPa
i calculated bulk modulus for 0GPa system by changing equilibrium
celldm(1) in range of -10% and +10% and calculatin energy. and used ev.x
for fitting. fiiting curve is an U-shaped plot

then i did the same procedure for 100GPa system by calculating energy
for the celldm(1) values -10% to +10%. first thing is: alatt vs energy
plot is not U-shaped. and if i extend the range from +-10%
to +-20% a get an equilibrium energy but obviously it is the same as
that of 0GPa's result.

that is the point that i am getting confused by.
and still curious about, what should i do to calculate a bulk modulus
for a system under 100GPa?

thank you

On 02/26/2012 03:18 PM, Stefano Baroni wrote:
> Why not? Bulk modulus is just the second derivative of the energy wrt volume (modulo some appropriate definition). Don't be fooled by names. If you are guided by concepts, rather than by names, it should be pretty clear what can be calculated and what cannot. If it's the second derivative of the energy wrt volume that you need, it should be obvious that it can be calculated and how. No matter what the name is. If it is something else, well it depends ... (on concepts, not on names). SB
>
> --
> Stefano Baroni, Trieste -- swift message written and sent on the go
>
>
>> hi,
>> mayb this is a stupid question but i wonder if is it possible to
>> calculate bulk modulus under different pressures? or is it meaningless.
>> i have seen some articles that gives pressure vs. bulk modulus data. but
>> it confuses me.
>>
>> thanks
>>
>> --
>>
>> * Dept. of Chemistry
>>   SUNY Buffalo
>>   NY,USA
>>
>> * Abant Izzet Baysal University
>>    Dept. of Computer Education
>>    Bolu,Turkey
>>
>> _______________________________________________
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--

* Dept. of Chemistry
SUNY Buffalo
NY,USA

* Abant Izzet Baysal University
Dept. of Computer Education
Bolu,Turkey

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