Re: questions of damping effect

["John J. Rehr" <jjr@leonardo.phys.washington.edu>]

Dear Dr. Zhao,

  The question you raise brings up a confusion between ground
state and excited state calculations. For ground state calculations
the X_alpha method with adjustable alpha was used to approximate
the exchange potential in a local density approximation. The
Kohn-Sham LDA was an improvement and predicted alpha = 2/3
for the exchange only term. BUT this is a poor approximation
for excited states since the exchange-correlation potential must
be replaced by an energy dependent self-energy which slowly
decays with increasing energy. This is automatically accounted
for by the default Hedin-Lundqvist self-energy (EXCHANGE 0)
in FEFF. See the FEFF document for details. So there's no
need to adjust anything. The Hedin-Lundqvist self energy is
not perfect - but it's often adequate. Other options like the
Dirac-Hara self-energy can also be used.

  
  With best wishes,
  John

On Sat, 30 Aug 2003, N. Zhao wrote:

> Hello Feff users,
>   I am now trying to simulate XANES for MgO.
> According to literature, when calculating its
> exchange potential, the multiplication factor
> ¦Á(alpha) should be 2/3. Does anybody know
> which code I should use to set up this value in
> feff.inp file? Should I use AFLOP? If yes, is
> 1.67 the value I should put after AFLOP?
>   Anthoer question is about damping effect. If
> I want to consider a -1.0ev damping, which code
> should I use?
>  Thanks in advance,
> Ni
> 
> 
> Ni Zhao
> Department of Materials Science and Engineering
> Mcmaster University
> 1280 Main Street West
> Hamilton, Ont. L8S 4L7, Canada
> (905) 525-9140 Ext. 24544
>