[Wien] Checking the effect of pressure on the bandstructure

amit ribak Thu, 07 May 2015 00:02:18 -0700

​Hello,

I'm interested in checking the effect of pressure (uni-axial) on the band
structure. I first calculated the band structure with and without
spin-orbit interaction and was able to restore previous results.
Now, I want to see how the pressure affects the band structure. How can I
incorporate this into Wien2k?

The c over a optimization is the way to do it or I simply need to change
the lattice parameters of the initial structure?

Best regards,
Amit

Reply:

1- from    Dr. Víctor Luaña

Re: [Wien] Checking the effect of pressure on the bandstructure

Víctor Luaña Cabal Thu, 07 May 2015 02:33:01 -0700

Amit,

1) Use thermodynamics

2) Your wien2k calculation is giving you the internal energy:
   E = U(S,V), nominally at 0K, no zero temperature effect, and 0Pa.

3) To analyze pressure effects you can analyze the enthalpy or the
   Gibbs funcion:

   H(S,V) = U + pV
   G(T,p) = U + pV -TS

   If you have enough information on the vibrations of your system try
   to study G, clearly. The zero temperature effect (ZPE, zero point
   energy) has not been deeply studied in this field of solid state.
   It is an interesting subject to explore better.

4) Look for papers in Phys Rev B on this subject. I have mine
   available, so forgive me for citing mainly my publications on this
   subject. The most recent are articles by Alberto Otero-de-la-Roza
   and myself. For example:
   Phys. Rev. B 84 (2011) 184103

5) On Computer Phys Commun you have freeware codes to do this task.
   Look for the gibbs, asturfit and gibbs2 programs.

6) Notice that the codes in (5) are truly devoted to hydrostatic
   conditions, no uni-axial situations. For that I would recommend
   analyzing the grand potential

   \Omegai(T,p,\vec{\mu}) = U +pV -TS - \vec{n} \vec{\mu}

   (Sorry for the tex jargon)
   If you want to analyze a pure substance, remember that
   $\mu = g = G/n$, and \vec{n} = n.

Best regards,
             Dr. Víctor Luaña

2- from Fecher gerhad




Re: [Wien] Checking the effect of pressure on the bandstructure

Fecher, Gerhard Thu, 07 May 2015 08:09:24 -0700




Hi Amit
You may calculate the single crystal elastic constants (sub-programs and 
scripts are available in Wien2k) to find out how the lattice parameters change 
under pressure.
If you apply pressure along some axis c, the remaining two axes a and b will 
also change, usually become larger, only in few cases they may shrink also with 
the pressure.
(Indeed, you can also check for changes in the lattice under shear or 
combinations of different mechanical stress)
Might be good to have some exprimental data of the material to check if the 
changes of the lattice under uniaxial pressure is correctly described.
If you have the new lattice parameters you can calculate the spaghetties as 
usual.

Temperature is bad, it will force occupation of phonons that cause an energy 
dissipation of the electrons.
This is , as far as I know, not implemented in Wien2k (maybe it is in some 
Greens function codes that allow for complex potentials with an imaginary part 
to simmulate the energy dissipation).
It will smear out the spaghettis.

Ciao
Gerhard