[Pw_forum] Fw: modified explicit exchange potential

[Helen]

I was wondering if anyone had some answers to these questions about exx.f90?
Thanks Helen
(Hebrew University, Jerusalem)
----- Original Message ----- 
From: "Helen" <helen at fh.huji.ac.il>
To: "degironc" <degironc at sissa.it>
Sent: Monday, July 23, 2007 2:48 PM
Subject: Re: [Pw_forum] modified explicit exchange potential


> Hi,
> Thanks so much for your reply. I've been looking through exx.f90 and there 
> are a few fundamental things I don't understand.
>
> 1. I've read Gygi's paper and I understand you convert the integral into a 
> term with no divergence and a diverging analytical term which can be 
> evaluated.
> Int g/(x-x0) => Int (g-g0)/(x-x0) + Int(g0/(x-x0))
> as is shown in equation (5) of the paper (PRB 34, 4405).
> However in the code it looks like you're just multiplying U by a 
> factor(8/7). How does this fit in with Gygi and where does 8/7 come from?
>
> 2. I still don't understand what exxdiv does/calculates?
>
> Thanks for your help,
> Helen