Subject: RE: G:G98 PES Optimization convergence / Convergence of DFT optimizations

From: "Stefan Fau" <[email-masked]>
Date: Sat, 16 Jan 1999 18:11:00 +0100

Dear Dr. Burger,

the degree of convergence of an optimized structure is _not_ related to the starting geometry. The starting geometry only affects the number of optimization steps required to reach the optimized structure.

Did you do DFT optimizations? In my ear it sounds like a problem of Gaussian DFT: In our group many DFT optimizations converge with very low forces and displacements close to the thresholds. Subsequent frequency calculations produce similar forces but displacements that are above the thresholds by sometimes disturbingly huge amounts.
We believe that this is due to extremely flat potential energy surfaces near the minima. On the other hand it could be a problem of the fit functions used in evaluating the XC-functional.

Would anybody like to comment on the issue of convergence criteria with DFT optimizations?

Stefan
___________________________________
Dr. Stefan Fau
Fachbereich Chemie, AK Frenking
Philipps-Universität Marburg
35032 Marburg, Germany
[email-masked]