Subject: Re: CCL:Normal modes with ADF99

From: Marcel Swart <[email-masked]>
Date: Thu, 6 Jan 2000 18:00:36 +0100

>Good Morning and best wishes to all the Scientist Community !
>
>I have some problems with frequencies calculations with ADF 99. I obtain a
>lot of imaginary modes even if the structure seems to be optimized (I have
>already successfully performed the jobs at HF level). Could someone help me,
>giving some advices about displacements to use (cartesian vs z-mat),
>symmetry or numerical precision ?

First of all. ADF 99 is a DENSITY FUNCTIONAL program (i.e. the Amsterdam
Density Functional program). Everyone knows that DFT gives better
geometries than HF, and the geometries from DFT are generally different
>from HF ones. Simply because HF lacks electron correlation which IS present
in DFT.

The fact that you get imaginary frequencies indicates indeed that you do
NOT have an optimized geometry. So, I suggest that you first optimize the
geometry with ADF99 (CONVERGE grad=1.0e-5), which should not be too
difficult, because ADF99 is a fast, accurate and parallel program.

Secondly, in the frequencies run, you should use an integration accuracy of
at least 6.0, but I personally prefer even higher values. After you have
done this, and still get imaginary frequencies, come back for more advice.

>The second question is is there any programm that allows me to visualize the
>normal modes ? We are using the Cerius 2 package, but the new TAPE21 files
>aren't compatible with our version of Cerius 2.

Check the ADF homepage (http://www.scm.com) because they include some
support for Cerius.

Best regards,

Marcel Swart
=========================================
drs. Marcel Swart

Theoretical Chemistry (MSC)
Molecular Dynamics (GBB)

Rijksuniversiteit Groningen
Chemistry Department
Nijenborgh 4
9747 AG Groningen
The Netherlands

tel : +31 - (0)50 - 3634377
fax : +31 - (0)50 - 3634441

E-mail : [email-masked]
WWW: http://hydra.chem.rug.nl/~swart/
=========================================