Subject: Problems with HOMO/LUMO gap

From: [email-masked]
Date: Tue, 28 Mar 2000 09:47:59 +0000

Hi there all,

a question which has been as issue for some time which I seem to be stuck
with is the problem of getting SCF convergence when there is a small
HOMO/LUMO gap. The program that we are using is DMol3 by MSI.
Specifically the problem relates to structural optimisation of actinide
containing molecules - especially those which are not "stable" (e.g. UF4H).
There are several procedures which are recommended to get around this
including smearing the orbitals (to allow partial occupancy) and level
shift (where the vitual orbitals are just moved out of harms way). However
neither of these methods seems to improve convergence more than marginally
(they may converge once or twice but usually fail as the structure nears an
optimum geometry).
Has anyone any experience with other systems which do not converge for
similar reasons? If so what did you find that solved the problem or helped
at all?

Thanks - I will summarise for the list if I get any replies.

Scott Owens
[email-masked]