[Wien] temperature-dependent elastic constants

[Peter Blaha]

I don't think that this is the way to proceed. You suggest to take into
account only the "electronic temperature" via the Fermi function. Remember,
300K is only 2 mRy, so unless you go to very large temperatures, your
Fermi-function effects will be very small.

Unfortunately, in general this is a very small contribution and most likely
does not produce the effect you want to investigate.

For sure the thermal expansion is "more" important and you need to consider
this effect.

The best procedure is most likely to calculate the full phonon-dispersion
and I think from the slopes of the acustic modes you can get your info.
Using a "quasi-harmonic" approximation you can calculate the temperature
expansion "ab-initio" too and see how the slopes change with temperature
(volume). Of course such calculations are a bit expensive, but doable.
 

> I have calculated some elastic constants for cubic metals using the "elast"
> package of Wien2k. I am mostly interested in the shear modulus, which came out
> in pretty good agreement with experimental values. So far I have been using
> the tetrahedron integration method in lapw2. I was wondering wether it would
> make sense to try and calculate the temperature-dependence of these elastic
> constants using the Fermi smearing technique, with varying smearing
> temperatures? I guess I could also introduce the thermal expansion 'by hand',
> by modifying the structure.
> Are there fundamental limitations to this approach or caveats I should be
> aware of?
> Thanks in advance for sharing your experience or insights.
> 
> Olivier.
> 
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                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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