Subject: CCL: CCL:Optimization in transition state

From: Ramon Crehuet <rcsqtc|at|iiqab.csic.es>
Date: Wed, 27 Oct 2004 09:23:39 +0200

Dear  Arvydas Tamulis,
    A Transition State (within the Transition State theory) is a 
stationary point (gradient=0) having hessian matrix with one negative 
eigenvalue. The Gaussian TS search algorithm needs to start from a 
region where this negative eigenvalue already exisits. Otherwise it 
cannot follow an eigenvector to the desired stationary point.
    Your initial point is not in this region, either because your guess 
is too crude or because the level of theory you are using now gives a 
different potential energy surface from the one you used to generate the 
guess (e.g. you initial geometry is a localised TS in a smaller basis set).
    Having said that, you can force Gaussian not to check for the number 
of negative eigenvalues with the flag Opt=(NoEigenTest , ...)  but the 
chances of success are slim. Consder also giving an initial hessian from 
a previous successful optimisation.
Best regards,

Ramon Creguet

Arvydas Tamulis wrote:

> Dear Colleagues,
>
> Would you please to help me because received unexpected stop during 
> optimization in transition state of biological derivatives applying 
> Gaussian03.
> The input line is follows:
>
> #P B3LYP 6-31G Opt=(TS,ModRedundant) IOp(6/3=12) DIIS SCFCYC=120
>
> The optimization started, but after one cycle stopped:
>
> Optimization stopped.
>     -- Wrong number of Negative eigenvalues: Desired=  1 Actual=  0
>     -- Flag reset to prevent archiving.
>
> My question is: what does it means these comments in G03 and how to 
> avoid this stopping?
>
> Best regards, Arvydas Tamulis
>
>
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Date: Tue, 26 Oct 2004 12:36:10 -0500 (EST)
Subject: semi-emprical QM compter program for periodic systems?
From: korkin~at~nanoandgiga.com
To: chemistry~at~ccl.net

Dear Coleagues,

I am looking for the software program(s) to describe periodic systems (not
molecuar type clusters!) such as Si-SiO2 interfaces on the level of
semi-empirical quantum chemistry. There are plenty of different empirical
force fileds which obviously work in a very narrow area of application
limited for classical mechannics and there are numbers of ab-initio (or ab
initio like for those who want to distibguish these two definitions) DFT
codes but there is seems to be a shortage of unexpensive QM methods and
computer programs (!) for periodic systems, which are based on or similar
to NDDO based methods popular in the molecular world. Transition metal
systems or ionic crystals are not well suited for NDDO type methods while
Si-SiO2 is on the edge and I believe some NDDO-like methods may still be
cheap enough and reasonable enough as a first approximation for a variaety
of properties accessible for QM methods within one calucation [including
geometry optimization] such as strcture, geometry and electronic
properties. Any pointers to the software programs of this kind will be
very much appreciated as well as general advises and comments.

If there is enough interest I will send my summary back to CCL.
Since I am not at the CCL list and watch it only via web interface,
please, copy your response directly to me to my yahoo e-mail
( a_korkin~at~yahoo.com )

Best regards,
Anatoli Korkin
a_korkin~at~yahoo.com