[Pw_forum] doing QHA calculations (contd)

[Eyvaz Isaev]

In this case I guess you can not calculate the free
energy. I am aware that somebody just neglected this
(imaginary) part when they got imaginary frequences,
but the correctness of this approximation is under
question, in my personal opinion. At least, you can
calculate zero point energy. 

Bests,
Eyvaz.  

--- Tuhina Kelkar <tr.kelkar at ncl.res.in> wrote:

> It struck me with your mention of ln(nu)... a lot of
> my initial nu(i) values are negative.  Am I doing
> something wrong? Would it be ok to just discard
> these values? 
> -Tuhina
> >Hi,
> >start  a loop (over nu) in fqha.f90 from 2 instead
> of
> >1. nu(1) is zero, so, ln(nu) is not defined.
> >Bests,
> >Eyvaz
> --- Tuhina Kelkar
>
<<../../servlet/Compose?To=tr.kelkar at ncl.res.in>tr.kelkar at ncl.res.in>
> wrote:
> > I checked my .phdos and found that the nu(i)
> values
> > are very large. That is why even after commenting
> > the "wrong grid" line in fqha.f90 and recompiling
> > (as suggested by Eyvaz) I am getting Ftot as NaN
> in
> > the output.
> > Where am I going wrong in the phonon DOS
> > calcuations? What can I do to rectify this? Could
> > you suggest some books and papers that I could
> refer
> > to develop a better understanding of phonon DOS
> and
> > quasi harmonic approximation?
> > Regards,
> > Tuhina
>
---------------------------------------------------------------------------------------------------------------
> Tuhina Kelkar
> Junior Research Fellow
> Physical Chemistry Division,
> National Chemical Laboratory,
> Pune - 411 008
> INDIA
> Contact: 020-25902298
> alternative email: tuhina at gmail.com
>
---------------------------------------------------------------------------------------------------------------
> 


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