From chemistry-request@www.ccl.net Sat Jan 16 12:09:56 1999 Received: from sg1503.chemie.uni-marburg.de (root@sg1503.Chemie.Uni-Marburg.DE [137.248.151.215]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id MAA23087 Sat, 16 Jan 1999 12:09:55 -0500 (EST) Received: from pc15105 (pc15105.Chemie.Uni-Marburg.DE [137.248.151.180]) by sg1503.chemie.uni-marburg.de (8.9.2/8.9.2/schn) with SMTP id SAA14820; Sat, 16 Jan 1999 18:09:47 +0100 (MET) From: "Stefan Fau" To: "CCL" Subject: RE: G:G98 PES Optimization convergence / Convergence of DFT optimizations Date: Sat, 16 Jan 1999 18:11:00 +0100 Message-ID: <000a01be4173$30f59d40$b497f889@pc15105.chemie.uni-marburg.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook 8.5, Build 4.71.2173.0 In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 Importance: Normal Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by www.ccl.net id MAA23088 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 fau@chemie.uni-marburg.de