[Ifeffit] FEff

Matt Newville newville at cars.uchicago.edu
Mon Sep 29 12:47:57 CDT 2014

On Mon, Sep 29, 2014 at 11:48 AM, Bruce Ravel <bravel at bnl.gov> wrote:

> On 09/29/2014 11:44 AM, Carlos Triana Estupinan wrote:
>> Dear
>> Feff group
>> I am Carlos Triana, and I want ask you the following.
>> I am trying to calculate the feff.inp file for a theoretical amorphous
>> structure composed by a supercell with 24 Ti atoms surrounding by 48
>> oxygen atoms with different coordination. In amorphous materials or
>> materials with distortions from regular crystals, the absorbing atoms
>> may have different surroundings.
>> My question is how can I build the feff.inp file in this case, shall I
>> define the 24 Ti atoms like absorbing atoms, because in this case the
>> feff does not works.
>> What can I do in this case, how can I build the feff.inp file with
>> different environments
>> I will be very grateful for your help
> I'd like to follow up on Matt's comment.
> I presume you have some way of knowing a list of Cartesian coordinates for
> the atoms in your cluster.  If so, the discussion on pages 7-10 of this
> talk should be helpful, with the caveat that your input file needs to be
> appropriate to the version of Feff you intend to use.
> https://speakerdeck.com/bruceravel/modeling-non-
> crystalline-samples?slide=9
> Make one input file for each Ti atom serving as the absorber.  As Matt
> said, take care not to overwrite your results.
> Were this my problem, I would prefer to organize and perform N
> calculation, then add them up myself.  That said, Feff does provide a
> simple sort of configuration average.  Look up "CFAVERAGE" in the Feff
> document.
> B

I believe CFAVERAGE does not work as advertised.  I haven't checked this
recently, but my recollection is that using CFAVERAGE always ends up giving
a coordination number that is a whole number, which cannot always be the
case.  That might depend on versions of Feff, and I'd be happy to shown to
be wrong about this.

Can anyone else verify or shed light on this?

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