Simon,
Could you be more specific about what does not
converge, the SCF or geometry optimizations?. If the SCF fails to
converge, then a geometry optimization will likely fail also.
If the
issue is thae SCF will the SCF converge at the HF level with a simple basis such
as STO-3G or 3-21? Do the HOMO and LUMO orbitals swap around during
the SCF? Does level shifting help?
Regards,
John McKelvey
On
Tue, Aug 5, 2008 at 3:29 AM, Simon Halstead shalstead .
hit.edu.cn <owner-chemistry**ccl.net> wrote:
Sent to CCL by: "Simon Halstead" [shalstead:hit.edu.cn]
Dear all,
I am trying to optimize some bridged (1-4) cyclohexane rings. I initially
optimized them using sempiempirical methods. These calculations converged very
rapidly. However, I then tried to optimize the resulting structures at a higher
level of theory. These high level calculations have failed to converge, despite
being run for a large number of steps. I have tried HF, MP2 and B3LYP with a
variety of basis sets but nothing appears to converge. Visualizing the outputs
of the failed calculations shows no problems with the structure.
Does anyone have any experience with structures like this or can anyone give me
a suggestion of how best to optimize bridged rings?
I am using GAMESS if this makes any differnce.
Thanks for your help,
Simon Halstead
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