[Pw_forum] Questions about Thermal properties calculation

[Eyvaz Isaev]

Dear Bob,

Well, let me start to answer questions raiesed.

--- On Sun, 8/9/09, john Bob <bobjohn.lzu at gmail.com> wrote:
 
>  
> Q1: Does pwscf have tools to calculate internal
> energe, specific heat, entropy? Though I find
> fqha.x. Should I modify it to calculate the other
> properties myself?

fqha.f90 is somewhat obsolete and was considerably enhanced in fqha.f90 from QHA package. QHA can calculate more you can expect.

> Q2: I have a system with soft mode (negative phonon
> freq) in phonon dispersion. Is it meaningful to calculate
> these thermal properties. If it still have physical meaning,
> how to deal with the DOS below zero, abandon it or just add
> into the integration?

You have imaginary phonon frequencies, not negative, i.e. \omega^2<0. As concerns calculation of thermal properties when you have soft (imaginary) modes, I think the trick you suggest is not correct.  
  
> Q3: Using matdyn.x to get the full phonon dispersion,
> there are some discontiguous in phonon bands. Is there a
> convenient way to get continual phonon dispersion?

Most likely you have a semiconductor, so, you have LO-TO splitting at the \Gamma  point. If you have these discontinious at q-points different from \Gamma, your q-path is incorrect. 

Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com