[Wien] Thermal properties
Stefaan Cottenier
Stefaan.Cottenier at fys.kuleuven.ac.be
Wed Sep 17 09:22:22 CEST 2003
> (1) In our input file(case.struct), we have no option for defing
> temperature. If we want to calcualte thermal properties of crystals,
> How can we define temperature in WIEN2k???
As in all other DFT codes, this is *not* possible in a direct way (DFT in
its current implementations is a ground state method). Some tricks or
extensions in order to cure this are:
* Use TEMP in case.in2 instead of TETRA (this is just an a posteriori use of
a fermi distribution at T>0, and hardly corresponds to a physical
temperature).
* Use molecular dynamics (min_lapw), where you can set a temperature. This
requires large unit cells and many, many calculations before you reach
thermal equilibrium (if you reach it at all).
* Use wien2k together with the PHONON code by K. Parlinski, which gives you
a way to obtain some T-dependent properties (free energy, for instance).
> (2) How can we calcualte internal energy of any crystal structure
> using WIEN2k??? we want to calculate bulk properties for crystals
> having crystal structure other than cubic. eg. orthorhombic,
> rhomohederal. For calculating cold pressure we can use this formula
> P (cold) = d(E_in)/dV
> E_in internal energy, and V volume of the unit cell and than bulk
> modulus, we can calulate.
I don't understand what you mean? In case.struct, you can define any crystal
structure. Total energy (at 0 K) is always given by :ENE, volume always by
:VOL. A murnaghan fit in order to obtain the bulk modulus is done by eosfit.
Stefaan
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