Diagonalization error, overlap matrix not positive definite

[fangyongxinxi]

Dear Sir,
I try to use Extended Huckel method to calculate the energy of a system with ATK11.8.2. This calculation could be finished by ATK-DFT, but fail wihen I use ATK-Extended Huckel. The scripts are the "se_input.py" and "dft_input.py", all calculation parameters are set as default values.
when running the "se_input.py", the software shows :

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** Back Engine Exception 541 : Diagonalization error, overlap matrix not positive definite. This may be caused by atoms that are too close to each other or situated in equivalent positions, or (in the Extended Huckel model) a too low value of interaction_max_range
** Location : mathutils.cpp:1068

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
####

So, my problem is:
1. why this system could be finished by DFT, but not for SE? should I change some parameters in the SE calculation, such as basis set or something else? Is there some rules to choose the parameters in SE method ?


Thanks.

[Anders Blom]

The error message holds the key to the solution. Increasing the interaction max range to 20 Ang seems to work.