Increase NOVP error message meaning

[Paul Fons <paul-fons@aist.go.jp>]

  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@aist.go.jp

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