CCL: Ab initio on bridged rings

From: errol lewars <elewars---trentu.ca>
Subject: CCL: Ab initio on bridged rings
Date: Tue, 05 Aug 2008 16:25:25 -0400

 Sent to CCL by: errol lewars [elewars||trentu.ca]
 2008 August 05

Could you give us the structure (cartesians) of one (preferably thesmallest) of your troublesome conmpounds)?

 E. Lewars
 =============
 Simon Halstead shalstead . hit.edu.cn 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>