Subject: Atom-Atom partitioning of El. Energy

From: Patrick Bultinck <[email-masked]>
Date: Mon, 25 Apr 1994 14:25:12 +0200 (MET DST)

Hello world,

To my knowledge there is no option for GAMESS (US) to do atom-atom 
partitionings of the electronic energy.
By this partitioning I mean that the total electronic energy, as can be 
obtained using the classic (i.e. well known) RHF formula, is split up 
into different atom-atoms terms (i.e. atom1-atom1, atom1-atom2, and 
atom2-atom2 for a binuclear molecule.)
Because I thought it might be interesting for me to have a look at these 
terms, I headed off to find out if I could not write a small program to 
do this, or to change the FORTRAN code of gamess (US) as to fit my needs.

However, I am not an experienced programmer in FORTRAN (yet). So I ran 
into trouble (I have studied the first part of my first book on FORTRAN 
for the first time), so it is not easy for me change the GAMESS code.

Here is what I did...

I have always been programmig in Basic, or Pascal or C(++), or some even 
more exotic languages, so as we have a RS6000 workstation I started 
writing a C program.

I have changed the NPRINT=3 option in the GAMESS code and the rungms 
executable, so that files are saved with the density, fock and hcore 
matrices.

These files are read in by the program and changed as to yield some 
temporary files that may be used in calculations.

So when I now make a calculation I specify NPRINT=3 and get the normal 
output file plus a $JOB.at file in which I find the atom-atom parts.

Everything is written in a very simple C program, because I needed the 
results asap, so I did not care for any mumbo-jumbo optimising, or 
elegance (except for the elegance of using indents and such).

All this stuff has been done on the 1991 version of GAMESS (they wouldn't 
let me change the new one.)

My question is now : does anybody have an example of a calculation (with 
at least 10 **ten** basisfunctions) so that I can control my results.
I have confronted my findings with some theoretical facts that have to be 
obeyed, and they do obey...( I off course need to know which Basis Set is 
used...)

So if anybody could fax me a result, or if anybody has a reference to an 
article in which the atom-atom splittimgs are proposed, I would be very 
grateful if she/he could inform me on this matter...

P.S. when I have studied the whole FORTRAN book I will try to change the 
1993 version in the right way (namely through the FORTRAN code of GAMESS(US)).

Any help is mighty welcome,

Regards,
|-----------------------------------------------------------------------|
|     C-C                       Patrick Bultinck                        |
|    /   \                      Dept. Physical & Inorganic Chemistry    |
| C-O     O-C                   Section Quantum Chemistry               |
| |         |                   University of Ghent                     |
| C-O     O-C                   Krijgslaan 281 (S-3)                    |
|    \   /                      9000 Gent                               |
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