negative homo - lumo gap

[marci]

Hi Claudio,

typically this is an indication  that your system is metallic and that
the
selected optimization procedure  (OT) is not suitable. You may try to
use diagonalization
as optimization scheme, adding more MOS and smearing the occupation
numbers around the Fermi energy.
Regards
Marcella

On Nov 22, 12:13 pm, Claudio <marg... at gmail.com> wrote:
> 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!
>
> Claudio