[Pw_forum] Re: Calculating generalized susceptibility with PWscf

[stewart at cnf.cornell.edu]

Hi Stefano, 

The generalized susceptiblity I'm interested in appears in discussions of 
nesting vectors in Fermi surfaces.  It can be expressed in rough latex 
format as 

Chi(q) = \Sum_{ij,k} \frac{f(\eta_{k,i})[1-f(\eta_{k+q,j})]} {\eta_{k+q,j - 
\eta_{k,i}} 

where f is the Fermi function, \eta is the energy for the given band and k 
point, i and j are band indices.  Only bands that cross the Fermi energy are 
included in the sum.  I can send you a pdf file with the equation if the 
above is still unclear. 

I am putting together a small code to calculate this based on PWscf results, 
but I wanted to make sure that this wasn't available as a feature of PWscf.  
No sense in reinventing the wheel... 

Thanks, 

Derek
 

Stefano Baroni writes: 

> 
> On Sep 25, 2006, at 3:11 PM, stewart at cnf.cornell.edu wrote: 
> 
>> Hi everyone,
>>  I was wondering if it is possible to calculate the generalized  
>> susceptibility, chi(q), with the PWscf code.
> 
> what is a "generalized susceptipility"? 
> 
> PHONON can calculate the macroscopic dielectric constant "out of the  
> box". With little work one could obtain the G/=0 components of the  
> response to an applied electric field (q->0). With some more work, it  
> would not be difficult to calculate epsilon^{-1}(q,q) (I understand  that 
> my notation may not be more clear than yours ;-) 
> 
> S. 
> 
>> If someone could point me to the relevant documentation or  examples, I 
>> would greatly appreciate it.
>> Thanks,
>> Derek 
>> 
>> ################################
>> Derek Stewart, Ph. D.
>> Scientific Computation Associate
>> 250 Duffield Hall
>> Cornell Nanoscale Facility (CNF)
>> Ithaca, NY 14853
>> stewart (at) cnf.cornell.edu
>> (607) 255-2856
>> _______________________________________________
>> Pw_forum mailing list
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> 
> ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
> Trieste
> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) 
> 
> Please, if possible, don't  send me MS Word or PowerPoint attachments
> Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html 
> 
>  
> 
 


################################
Derek Stewart, Ph. D.
Scientific Computation Associate
250 Duffield Hall
Cornell Nanoscale Facility (CNF)
Ithaca, NY 14853
stewart (at) cnf.cornell.edu
(607) 255-2856