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 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