From owner-chemistry@ccl.net Wed Apr 20 16:39:00 2011
From: "Thomas Manz thomasamanz(-)gmail.com" <owner-chemistry++server.ccl.net>
To: CCL
Subject: CCL:G: problem with geometry optimization in g09
Message-Id: <-44438-110420163531-8566-UEV7XlG0nNEERBhDeWTEiQ++server.ccl.net>
X-Original-From: Thomas Manz <thomasamanz . gmail.com>
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Date: Wed, 20 Apr 2011 16:35:22 -0400
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Sent to CCL by: Thomas Manz [thomasamanz!A!gmail.com]
Hi Walter,

An sto-3g or 3-21G basis set is extremely small, so unless your system
contains more than a few hundred atoms it's probably not an
appropriate choice.
The 6-311++G** or another triple zeta basis set with polarization and
diffuse functions would be a better choice if your system contains
fewer than about 200 atoms.
Generally speaking, you would be better off using a correlated
electron method like density functional theory (e.g., B3LYP) than a
semi-empirical or hartree-fock calculation.
If your system contains hundreds of atoms, consider using a pure DFT
functional like PW91PW91 with a density fitting basis set (e.g.,
PW91PW91/6-311++G**/auto).
Unless there is a compelling reason to keep the Fe atoms fixed, why
not relax the whole structure?

Route line of the following type might be suitable:

# opt B3LYP/6-311++G** scf=(fermi,maxcycle=400)

You can find further instructions for how to perform a calculation of
this type in the Gaussian manual at www.gaussian.com.

Sincerely,

Tom

On Wed, Apr 20, 2011 at 10:32 AM, Walter Ca on wcanon[]ciq.uchile.cl
<owner-chemistry^_^ccl.net> wrote:
>
> Sent to CCL by: "Walter  Ca  on" [wcanon ~ ciq.uchile.cl]
> Hi, my name is Walter and we have the following problem.
> we are trying to perform a partial geometry optimization of some hydrogens atoms using g09, in a system with 3 Fe(III) atoms, in wich those 3 Fe(III) atoms are fixed. the system have charge +3. I have try from semi-empirical methods to UHF with some simple basis set like sto-3g or 3-21G, because i only want to optimized hydrogens atoms.
> Can anyone help me to try to fix this problem.
> Thanks
> Walter>      http://www.ccl.net/cgi-bin/ccl/send_ccl_message>      http://www.ccl.net/cgi-bin/ccl/send_ccl_message>      http://www.ccl.net/chemistry/sub_unsub.shtml>      http://www.ccl.net/spammers.txt>
>
>