From owner-chemistry@ccl.net Thu Apr 16 10:31:00 2009
From: "=?gb2312?B?yqnBvA==?= shiliang/./mail.ustc.edu.cn" <owner-chemistry=-=server.ccl.net>
To: CCL
Subject: CCL:G: geometry optimization convergence problem
Message-Id: <-39091-090416102813-9538-6dtiy4uxCAkbua1JnR+NRg=-=server.ccl.net>
X-Original-From: "=?gb2312?B?yqnBvA==?=" <shiliang(0)mail.ustc.edu.cn>
Content-Type: text/plain
Date: Thu, 16 Apr 2009 22:28:54 +0800


Sent to CCL by: "=?gb2312?B?yqnBvA==?=" [shiliang]~[mail.ustc.edu.cn]
Dear Alexander:

Below methods might be helpful:

1. Change initial geometry according to the oscilliation situation by using
Gaussview or other software.

2. Considering your PES might be flat, IOp(1/8=N) might take effect. (See
Gaussian.com)

As for GDIIS, I have not used it but Gaussian03 online manual writes: Recommemded
for use with ... molecules with flat potential energy surfaces.

Hope some method will work. Good luck!

Liang Shi



在您的来信中曾经提到:
>From: "Alexander Hoepker achoepker]*[gmail.com" <owner-chemistry]|[ccl.net>
>Reply-To: "CCL Subscribers" <chemistry]|[ccl.net>
>To: "Shi, Liang " <shiliang]|[mail.ustc.edu.cn>
>Subject: CCL:G: geometry optimization convergence problem
>Date:Thu, 16 Apr 2009 09:08:53 -0400
>
>Dear CCL community,
>I am having difficulty with a particular geometry optimization using
>B3LYPlevel of theory using a
>6-31G(d) basis set while constraining a bondlength using the
>ModRedundantkeyword in Gaussian. The geometry sequence energies drop
>nicely but then
>plateau at an average value while oscillating endlessly without ever
>converging. The Maximum and RMS Forces have converged whereas the
>Displacements have not. Would GDIIS help with this?
>Any suggestions would be very much appreciated.
>
>Thanks,
>
>Alexander Hoepker
>Cornell University
>Department of Chemistry and Chemical Biology