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Re: trouble with feff8
Dear Michel,
The trouble with feff8 you encountered is common for feff8, so
I sent my reply to you also to all feffusers.
First, the problem always will occur if someone tries to calculate
LDOS below interstitial potential (V_int=-21.5 for Fe) with
ZERO broadening. In that case the "photoelectron" wave vector k
is purely imaginary, Re(k)=0 and subroutines for bessel functions
are set to do calculations only for Re(k)>0. A simple fix in this
case is to add small NONZERO broadening: e.g.
LDOS -25 -20 0.01
seems to fix problem in your input file.
Also feff8 even with small broadening sometimes gives negative LDOS within
about 0.5 eV from the V_int. It is purely numerical error that arizes
for |k|<<1. The calculation are done so that some finite number is
obtained by divizion of two numbers close to 0. (i.e. A=0/0).
The algorithm needs to be changed for |k|<<1 region. We will fix that
later.
Let me know if addition of small broadening helps your calculations.
Best wishes
Alex Ankudinov
On Thu, 14 Nov 2002, Michel Jaouen wrote:
> Hi Alex,
>
> I have found a strange (for me!) problrm with feff82. I want
> to calculate the ldos for Fe with a high precision to compare to the
> results I obtain with Wien2k. So I run the code per piece : it gives
> a new Fermi level at about -11eV so that to obtain the bottom of the
> s-dos I must calculate the ldos between -25 and -20 eV. In that case
> I obtain a strange error (see the file enclosed). I must say that it
> works in the energy range -20 up to 20 eV, but it seems to fail under
> -20 eV. Is there a limitation in the code? I join the feff.inp file I
> use for running the code on our cluster (16 nodes) using the parallel
> version. Any solution?
>
> Best regards,
>
> Michel
>