negative homo - lumo gap

Claudio marg... at
Sun Nov 22 11:13:06 UTC 2009

Dear all,

sometimes after I converge a calculation to an accuracy of say 1.0E-5
I get things like

HOMO - LUMO gap [eV] :   -0.980594

This is because the Homo Energy is 0.22417642 and the Lumo Energy is
0.18814027 in AU.

I have requested the same accuracy for homo and lumo  and have added
enough iterations to the lumo calculation loop to make sure the
program claims it is converged. I am using the OT method. How do I
prevent this from happening? I mean how do I ensure that the
calculation yields Lumo energies that are higher than the homo energy?

Sorry to bother you and thanks for your help!


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