Trouble-Shooting FEFF Problems and Bug Reports


Appendix E: Trouble-Shooting FEFF Problems and Bug Reports

FEFF9 has been extensively tested on many different architectures, but occasionally new bugs show up. In an effort to maintain portable and trouble-free codes, we take all bug reports seriously. Please let us know if you encounter any compilation error or warning messages. Often we receive reports by users of older versions of feff of bugs that have been fixed in more recent releases. Other code failures can often be traced to input file errors, sometimes quite subtle, and some are compiler bugs, for which we try to find a workaround.

To report a bug, please tell us the version of the code you are using and which operating system and compiler you have. Please include a `feff.inp' if the problem occurs after compilation and enough detail concerning the warning or error messages or other difficulties you have so that we can attempt to reproduce the problem.

Some known and commonly encountered difficulties are:

  • 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".

  • An error in assigning potential indices; the first atom with a given potential index must

have the geometry representative of this potential type. This is sometimes fixed by using a somewhat larger cluster; in fact it is usually desirable to have a larger cluster for potential construction than that used in the XAFS calculation due to errors in the potentials at surfaces. Unless the atom distribution is physically possible, you can expect the code to have problems.

  • Hash collision in the pathfinder. This is now rare, but can usually be corrected simply

by changing distances in the fourth decimal place.

  • For the MIV and higher edges you may receive the error message like: Lambda array

overfilled. The calculations should be repeated with IORDER -70202 card.

  • For systems with a large number of potentials (eg. adamantane, a system of C and H

containing 26 different potentials) small negative numbers occur during the SCF calculation (negative density warning) and the DOS calculation (negative "`noise"' in the ldos). This is due to precision problems in the FMS routines with so many different potentials, and probably also more likely for very light atoms. For reasons of efficiency, the FMS routines work in single precision. One can eliminate the negative numbers by recompiling FEFF using double precision as default for real numbers (eg. using the -r8 option for the ifort compiler). However, this will make the calculation significantly slower.

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