[Ifeffit] Increase NOVP error message meaning

[Paul Fons]

   I am trying to run feff on some chalcogenide structures that have 
rather nearest-neighbor long bond lengths, e.g.


> Bond search from target site: Te1
> ...found 6 atoms within 0.00 - 3.20 A of this site
>
> ------------------------
>        dist [Å]   atoms
> ------------------------
>    1.   3.0488      6
> ------------------------
> Bond search complete



When I use this structure in feff82, I get the rather mysterious error 
INCREASE NOVP:
>
>  Calculating potentials ...
>     free atom potential and density for atom type    0
>     free atom potential and density for atom type    1
>     free atom potential and density for atom type    2
>     free atom potential and density for atom type    3
>     initial state energy
>     overlapped potential and density for unique potential    0
>     overlapped potential and density for unique potential    1
>     overlapped potential and density for unique potential    2
>     overlapped potential and density for unique potential    3
>     muffin tin radii and interstitial parameters
> tell authors to INCREASE NOVP

Being an experimentalist, I did increase novp until the previous error 
message stopped, however this resulted in a core dump:

>  Calculating potentials ...
>     free atom potential and density for atom type    0
>     free atom potential and density for atom type    1
>     free atom potential and density for atom type    2
>     free atom potential and density for atom type    3
>     initial state energy
>     overlapped potential and density for unique potential    0
>     overlapped potential and density for unique potential    1
>     overlapped potential and density for unique potential    2
>     overlapped potential and density for unique potential    3
>     muffin tin radii and interstitial parameters
>  iph, rnrm(iph)*bohr, rmt(iph)*bohr, folp(iph)
>     0  1.76126E+00  1.74898E+00  1.01667E+00
>     1  1.71891E+00  1.63874E+00  1.12886E+00
>     2  1.35785E+00  8.69242E-01  1.15000E+00
>     3  1.78418E+00  1.76792E+00  1.02193E+00
>  mu_old=       nan
>  Done with module 1: potentials.
>  Calculating LDOS ...
>               LDOS calculation for specified grid
>  Calculating energy and space dependent l-DOS.
>  It takes time ...
>      potential type  0
> Segmentation fault (core dumped)

When running the equivalent file in feff6, I get the

>  Calculating potentials and phases...
>      free atom potential and density for atom type    0
>      free atom potential and density for atom type    1
>      free atom potential and density for atom type    2
>      free atom potential and density for atom type    3
>      overlapped potential and density for unique potential    0
>      overlapped potential and density for unique potential    1
>      overlapped potential and density for unique potential    2
>      overlapped potential and density for unique potential    3
>      muffin tin radii and interstitial parameters
>      phase shifts for unique potential    0
>    Hard tests failed in fovrg.
>   Muffin-tin radius may be too large; coordination number too small.
>      phase shifts for unique potential    1
>    Hard tests failed in fovrg.
>   Muffin-tin radius may be too large; coordination number too small.
>      phase shifts for unique potential    2
>    Hard tests failed in fovrg.
>   Muffin-tin radius may be too large; coordination number too small.
>      phase shifts for unique potential    3
>    Hard tests failed in fovrg.
>   Muffin-tin radius may be too large; coordination number too small.
>  Preparing plane wave scattering amplitudes...
>    nncrit in prcrit       9

This message seems similar to the troubleshooting section in feff8 for 
which it states:

• Non-physical, widely spaced distributions of atoms. Symptoms of this 
common problem are very large muffin-tin radii (see the header of any 
‘.dat’ file) and possibly a failure of the phase-shift program to 
converge. This gives error message hard test fails in fovrg.



How to I avoid this problem (obviously the crystal structure is a 
given!).  I tried the INTERSTITIAL card, but to no avail.  Any 
suggestions are welcome.

Dr. Paul Fons
Senior Researcher
National Institute for Advanced Industrial Science & Technology
METI
Center for Applied Near-Field Optics Research (CANFOR)
AIST Central 4, Higashi 1-1-1
Tsukuba, Ibaraki JAPAN 305-8568

tel. +81-298-61-5636
fax. +81-298-61-2939

email: paul-fons at aist.go.jp

The lines below are in a Japanese font

〒３０５−８５６８
茨城県つくば市東１−１−1
つくば中央第４
近接場光応用工学センター
ポール・フォンス主任研究官
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