[Pw_forum] Questions about Thermal properties calculation

[Kun Yin]

Dear Zhou Bo:

Please add your affiliation when you post email next time.

> 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?
>  
>  
Yes for internal energy. No for specific heat, entropy at present. As I
know fqha.x has bug until version 4.0.5. (Maybe fixed at version 4.1,
you should check it by yourself). We modified matdyn.f90 to calculate
thermal properties as we need. I think it is not so difficult if you
know how to do numerical integration. Alternatively, you can try qha
package provided by Eyvaz Isaev. Download at
https://qe-forge.org/projects/qha/


> 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?
>  
If you don't provide us what your system is, we can not answer negative
frequency is meaningful or not. Generally, negative frequency has two
reasons: numerical errors or unstable structure at your calculated
condition.  For the former case, the negative value should not far from
zero, and you can add acoustic sum rule (asr=.crystal.) to eliminate it.
For the latter case, negative frequency is meaningful. It shows the
structure you calculated is unstable at some direction. You should
analyze this 'soft mode' carefully.

For both cases, when you do integration, I THINK negative value should
be abandoned. 
 
> 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?
>  
Calculate different path once a time, then connect them together when
you plot. 

Or modify the matdyn.f90 to meet your need as I did. See matdyn2.f90 at
attachment. The original qpoint list in matdyn input file is replaced by
connected qpoint list of qpath. More details and sample input see
HowTo.pdf. Example output graph as pdc-pdos.eps. Because the attachment
size in this mailing list can not exceed 200 KB. So if you want other
files, send me a personal email for request.

Cheers,
 
Kun Yin
School of Earth Sciences and Engineering
Nanjing University
China

email: kyin.cn at gmail.com
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