Subject: Re: CCL:Question about semi-empirical vs. tight-binding methods

From: David Gallagher <[email-masked]>
Date: Sat, 12 Oct 2002 08:22:57 -0700

Hi Connie,

Cobalt parameters (and other transition metals) are now included for AM1, 
PM3 and PM5 in the latest version of MOPAC 2002 in CAChe 5.04. These have 
recently been developed by the author, J.J.P.Stewart. You can download a 
free evaluation version from 
http://www.cachesoftware.com/cache/cachedemo_win.shtml  Also, you can input 
your own parameters into this version using the keyword "EXTERNAL=FILENAME".

Regards
David Gallagher, Fujitsu

At 11:50 AM 10/10/2002 -0400, Connie Chang wrote:
>Hi --
>
>I'm trying to find the vibrational modes of a molecule (~100 atoms)
>which has the elements carbon, nitrogen, oxygen, and cobalt in it.  I've
>tried doing this through commercial programs such as Hyperchem and
>Gaussian, using the semi-empirical methods they provide (since the
>ab-initio methods are too computer-intensive); but I'm not getting
>sensible results.  I suspect that part of the problem is because of the
>presence of the cobalt.
>
>My advisor wants me to write my own code now with the logic that code we
>write would be completely under our control as to what variables we
>tweak...  My question is which method would be the best to do this.
>
>Are semi-empirical methods the same as tight-binding methods?  I know
>that in tight binding methods, you use parameters for the Hamiltonian
>matrix elements.  And that you need to find the specific parameters for
>the atom connectivity in your particular case.  For example, since I
>have a carbon bonded to a nitrogen for my molecule, I need to find
>parameters specific to carbon-nitrogen connectivity.  My question is is
>there a way in either the semi-empirical or tight binding methods where
>i would just need the parameters of the individual elements and there
>would be some systematic way for me to get the parameters *between*
>elements?
>
>Any suggestions, resources, etc. would be very helpful and appreciated.
>
>Thanks,
>Connie Chang
>[email-masked]
>
>
>
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