[Sax-project-users] Fwd: Re: GW calculation on organic semiconductor --1st

[marsamos at democritos.it]

----- Forwarded message from marsamos at democritos.it -----
    Date: Mon, 20 Apr 2009 11:00:02 +0200
    From: marsamos at democritos.it
Reply-To: marsamos at democritos.it
Subject: Re: [Sax-project-users] GW calculation on organic semiconductor --1st
      To: xiaoyinxie <xiaoyinxie at 126.com>

Dear user, we where already aware of such 1D problems! I perform some 
calculations on PPV, polyacetylene and polyethylene and found that for 
PPV the agreement with experiment is good instead PA and PE seems to 
behave abnormaly, in the way you already noticed. If you try a 
calculation with cohsex option instead of plasmonpole you will see that 
the results are completely different. We suspect that the problem comes 
from the way plasmon-pole is interpolating. In fact in strongly 
anisotropic systems the traditional way of doing plasmon-pole is not 
consistent. We are now working in a modification of the plasmon pole. I 
hope that for august (beginning of september) we will release a new sax 
version. But if you need the optical properties, i.e. to solve Bethe 
Salpeter equation and you prefer to have the results before I suggest 
to you to do the following:

Perform a DFT calculation with exact-exchange (this really give good 
results for the electronic structure, I test this for PA and PE). Then 
calculate with sax the screening (Polarizability and W), and then 
perform the Bethe-Salpeter calculation. This procedure is theoretically 
correct with the lesser approximation. As EXX is still experimental 
within espresso you will have to modify some things within the code (is 
very easy). Let me now and I give you the exact computational procedure.


Best regards

Layla


of this We are now studying polyacetylene  Quoting xiaoyinxie 
<xiaoyinxie at 126.com>:

> Dear Sax developers:
>   I am now doing GW calculation with Sax-1.0.0 , When I test the code 
> with examples (example3)by calculating the band gap of Silicon ,It 
> was running well, I got a reasonable bandgap of 0.98eV with 8*8*8 
> k-mesh .
>   Problem came out during I calculting the bandgap of P3HT 
> <poly(3-hexylthiophene)> which has 1-D long polymer chain 
> structure.As I increase the number of k-points ,The band gap 
> decreases relatively .  A  0.26eV band gap of which experimental 
> value is 1.9eV  was obtained with 12*1*1 k-mesh.
>  Similar  problem happens when calculating the band gap of polyacetylene.
>  I am not sure if I wrongly selected the parameters of GW calcultion 
> or SAX code does not fit calculating band gap of oranic 
> semiconductor(or some bugs exist) .
>  Hope you can give me some recommendation.
>  My input files are in the next Email titled <GW calculation on 
> organic semiconductor --2st>



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