[Wien] How to get lattice parameter as a function of pressure?

[Stefaan Cottenier]

> Can you tell me how to extract lattice parameter as a function of pressure?
> I didn't find it in case.eosfit as mentioned here
> http://www.mail-archive.com/wien%40zeus.theochem.tuwien.ac.at/msg04276.html

It would be trivial to do this for a crystal that is entirely determined 
by the volume (for instance, bcc iron): you calculate energy for a few 
volumes, do the Birch-Murnaghan fit by eosfit, look for the volume vs. 
pressure data in case.eosfitb, and convert the volume to lattice parameter.

It becomes somewhat more complicated when you have internal degrees of 
freedom (let's still assume a cubic crystal for the time being). Again 
calculate the total energy for a set of volumes. But for every volume, 
the internal positions should now be optimized first. Once you have done 
that, the procedure is the same as before, and you can get the lattice 
parameters out of the volume.

Now drop the requirement of a cubic crystal. Take an orthorhombic one 
(with or without internal degrees of freedom). Again you need the total 
energy for a set of volumes. But for every volume you need optimize 
internal parameters and the three lattice parameters (with the 
restriction that the volume is kept constant). From these optimizations, 
you will know what the relation between volume and the three different 
lattice parameters is. From the fitted volume-pressure relation, you can 
get any of the lattice parameters as a function of pressure.

Stefaan

>
> After x eosfit, in the case.eosfit, I can only find three colums, which
> I think corresponding to volum, energy and pressure. But no lattice
> constant information. I can't find any lattice constant information in
> case.outputeos either.
>
> I guess eosfit6 probably can do this job, however, I don't know how to
> use it. Before doing x eosfit, I did,  parabolfit_lapw,  but it always
> gives me errors. (see blow)
>
> I hope you can give me some idea. Thanks in advance.
>
> What I have already done,
> 1)  do x optimize and create 36 cases.
> 2)  run optimize.job with "save_lapw -d optimize ${i}" which saves all
> my data into directory optimize.
> 3)  grepline :ENE "optimize/*scf" 1 >> case.analysis
>        grepline :VOL "optimize/*scf" 1 >> case.analysis
> 4) eplot_lapw -t vol   This step gives me the plot Energy vs Vol.
> 5) x eosfit
> 6) parabolfit_lapw -t 2 -f optimize -scf 'optimize/*.scf'   : This step
> gives error like this
>
> ls: No match.
> ls: No match.
> optimize.ene and optimize.latparam generated
>    ERROR IN OPENING UNIT:          10
>          FILENAME:
>   ZrPSe.ene
>      STATUS: old          FORM:formatted
> OPEN FAILED
> 0.0u 0.0s 0:00.00 0.0% 0+0k 0+0io 0pf+0w
>
>
>
>
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-- 
Stefaan Cottenier
Center for Molecular Modeling (CMM) &
Department of Materials Science and Engineering (DMSE)
Ghent University
Tech Lane Ghent Science Park – Campus A
building 903
BE-9052 Zwijnaarde
Belgium

http://molmod.ugent.be
http://www.ugent.be/ea/dmse/en
email: stefaan.cottenier at ugent.be

my conference talks on Youtube: http://goo.gl/P2b1Hs
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