Subject: Geom. Optimization in Solvent (Gaussian, Jaguar)

From: Shaji Chempath <shaji..at..berkeley.edu>
Date: Thu, 04 Mar 2004 20:30:27 -0800

Hello CCLers,

Few weeks beore I had asked a question about geometry optimization in 
the presence of a solvent. I would like to thank all the people who 
replied to that. ( see summary of replies below). 

However I still have lots of problems with optimizing in the presence of 
solvent. I have used both Gaussian and Jaguar for doing my polarizable 
continuum optimizations and still no luck. 

Here is what I understand about what is going on, please let me know if 
you have any opinions. It appears as though the gradients calculated in 
the presence of solvent are far less accurate. This  may be because the 
'Poisson Boltzmann' equation is solved numerically for the solvent
region and the reaction field in the solvent is mapped on to limited 
number of "Tesserae" (points on the solute-solvent boundary).  This 
somehow makes the potential energy surface very rough, compared to the 
smooth surface in gas phase. Look at the graphs (on my webpage) to see 
what I mean

http://zeolites.cqe.nwu.edu/shaji/solvation.html

You can see that the gas phase optimization proceeds smoothly, but 
liquid phase optimizations run into bumpy potnetial energy surface. 
(even after staring from a gas phase optimized geometry). This is a 
general phenomena (the roughening of the potential energy surface) I 
have observed for different systems I have tried .

 So based on this I hav ecome to the conclusion that the optimization 
with solvent is very tough and works only for very simple molecules. Am 
I wrong?

Summary of help I got from others regarding PCM (Gaussian) optimizations
-------------------------------------------------------------

a) initially do a gas phase geometry and then start liquid phase
optimization from there

b) use "OPT(calcfc)" to calculate initial hessian

c) try iefpcm instead of pcm or scipcm

d) try "loose" optimization

e) try changing TSNUM (number of tesserae) or TSARE(ares of tesserae) in 
scrf

f) use nosymm option

Anyway none of them seem to have helped in particular for my molecules
Thanks again

Shaji