Subject: Hindered Rotor Analysis in G03

From: Matthias Lein <matthias|at|chemie.uni-marburg.de>
Date: Mon, 28 Jun 2004 11:17:34 +0200

Hi all,

investigating a molecule of 72 atoms I calculated the thermodynamical
data of dissociation given by standard frequency analysis of Gaussian98
(and G03).

Given one rotational barrier of about 10 kcal/mol I thought it to be
useful to try the "Freq(HinderedRotor)"-Keyword in Gaussian to correct
the data for contributions of internal rotation. I used an already
finished harmonic frequency analysis and the "readfc"-keyword to avoid
recalculation of the frequencies.

The algorithm of Schlegel et al. found two internal rotations but then
skipped the calculation with the following lines:

> Check for ring deformation
> Number of internal rotation degrees of freedom =   2
> NNew=  156 NTest=    2 NB=   45 IFrz=    0 IBar=    7 ICyc=    0
> Problem with the number of degrees of freedom
> Error termination via Link716

My questions:

1) Does anyone know the limitations of this keyword? (No of atoms,
degrees of freedom,...)

2) Is there knowledge about problems and performance of this method,
including numerical values (is it necessary or reasonable to use these
corrections)?

Thanks in advance
Matthias.