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Possible reasons for such behavior are not always clear, but they
typically fall into one of the following cases:
- serious error in data, such as bad atomic positions or bad
crystal structure/supercell;
- a bad PP, typically with a ghost, but also a US-PP with
non-positive charge density, leading to a violation of positiveness
of the S matrix appearing in the US-PP formalism;
- a failure of the algorithm performing subspace
diagonalization. The LAPACK algorithms used by cdiaghg/rdiaghg are
very robust and extensively tested. Still, it may seldom happen that
such algorithms fail. Try to use conjugate-gradient diagonalization
(diagonalization='cg'), a slower but very robust algorithm, and see
what happens.
- buggy libraries. Machine-optimized mathematical libraries are
very fast but sometimes not so robust from a numerical point of
view. Suspicious behavior: you get an error that is not
reproducible on other architectures or that disappears if the
calculation is repeated with even minimal changes in
parameters. Known cases: HP-Compaq alphas with cxml libraries, Mac
OS-X with system blas/lapack. Try to use compiled BLAS and LAPACK
(or better, ATLAS) instead of machine-optimized libraries.
Next: 7.8 pw.x crashes with
Up: 7 Troubleshooting
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Paolo Giannozzi
2009-10-01