Last Modified 17 January 2002

SCTB: Trouble Shooting

Version 0.80

There are several conditions when the sctb program will give nonsensical results. These occur when something in the crystal structure takes us outside the range of validity of the Slater-Koster parameters in the Tight-Binding Parameters Database. Two cases typically occur:

• In the first case, the overlap matrix of the Slater-Koster parametrization becomes unphysical, i.e., it develops a negative eigenvalue. This indicates that no actual set of wave-functions could produce this particular matrix. Typically this will occur when two or more atoms get close together. We are working on parametrization forms for the overlap matrix elements which will avoid this difficulty.
• In the second case, we exceed the range of the parametrization fitting and the energy behaves badly. Typically we see the total energy begin to decrease as we go to small volumes, even when the overlap matrix remains physical (positive definite).

If these situations occur, please contact the authors to determine if a better set of tight-binding parameters has been or can be developed.

If other errors occur, please examine your input files very carefully, using the Examples in the Usage section as a guide. It may help to change the debugging level in the tb.data file to 1, which will print out eigenvalues, or 2, which will print out some of the matrices used.

Of course, as much as we would like to, we cannot produce perfect code, even on the N^th try. We have therefore prepared a SCTB -Binding Software Trouble Reports page, where you can find information about bugs and bug fixes.

To report bugs in sctb, please send email to Noam Bernstein (bernstei@dave.nrl.navy.mil) at the Naval Research Laboratory. Describe the conditions that you found the bug. A (brief) sample input and output which replicates the bug will be very useful.

Finally, this manual has been checked (really). Please send any error reports to bernstei@dave.nrl.navy.mil.