[Pw_forum] equation of state fitting

Alberto Otero de la Roza aoterodelaroza at gmail.com
Wed Aug 16 19:18:55 CEST 2017

Hi Sunetra,

There are a number of other equations of state you can use. See for


and references therein. You can do the fit with a instead of V if you
want, but then note that you'll have to use the chain rule to write
E''(V) in terms of E'(a) and E''(a), and the expression will depend on
the V(a) function. You also need to make sure that E and V, which are
extensive quantities, correspond to the same number of
atoms. Otherwise, you'll be an integer factor off the correct result.



Dr. Alberto Otero de la Roza
Department of Chemistry, 
University of British Columbia, Okanagan
Kelowna, British Columbia, Canada V1V 1V7

* Sunetra Das <sunetra.das.88 at gmail.com> [2017-08-16 22:06:01 +0530]:
> Dear QE users,
> I would like to know if there are any other equation of state that we can
> use to fit the 'etot vs alat' graph to find out the equilibrium lattice
> constant. I have been following the QE tutorials to learn the basics where
> it has been demonstrated how to fit a etot vs alat graph using the four
> given equations of state. But none of the obtained equilibrium bulk modulus
> values from those equation fitting match the given experimental value, not
> even close.
> How to improve the fitting of the equations or is there any other equation
> I can use to fit the obtained data?
> I am new to QE, any suggestion is highly appreciated.
> Thank you.
> Regards,
> Sunetra Das
> Assistant Professor,
> MMC College, Kolkata, WB,
> India.

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