# G98 and SCRF

Hi,
I'm trying to optimize the structure of a simple silica compund
(H3SiOH) in THF solvent by means of SCRF calculation in
Gaussian 98. When I run the calculation with opt=(loose) and
SCRF=(cpcm,solvent=THF) the calculation converges in a couple
of steps. However, when I run the calculation with the standard
convergence criteria (or tighter) the calculation does never
converge. The energy remains oscilating (typically in the second
decimal), as does the force and displacements, and the calculation
typically exits with a L9999 error. Increasing the maximum number
of steps only causes the calculation to stop after more steps and
not the job to converge.
In both job files G98 warnes that sometimes some elements are
discarded. However, only in the tighter criteria run there are warning
that a certain electronic charge (in this case charge 144) has
positive or a negative charge ("Electronic charge 144 has a
negative value: -0.349460"). Could this screw up convergence or
are there other important details wich are important to insure
convergence in such SCRF calculations.
Cheers,
Martijn
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Martijn Zwijnenburg
Lab. of Applied Organic Chemistry and Catalysis
Delft University of Technology
Julianalaan 136
2628 BL Delft
The Netherlands
Tel: 0031-(0)152782691
Fax: 0031-(0)152784700
e-mail: M.A.Zwijnenburg (+ at +) tnw.tudelft.nl
web page: http://come.to/tock