[molpro-user] A question about the dummy atom in SAPT calculation in molpro

[Tatiana Korona]

Hi,

In SAPT, as implemented in Molpro by Hesselmann and Jansen your have to 
use a so-called dimer-centered basis set, i.e. you use the same basis for 
both monomers. This means that when performing monomer calculations you 
have to switch off another monomer, but you still need a basis set 
centered on that monomer (which is called popularly a "ghost"). This has 
nothing to do with BSSE. If you want to use monomer-center basis sets 
(i.e. different basis sets for monomers A and B), you need to use the SAPT 
program of Szalewicz et al. A numerical experience tells however that pure 
MCBS are not good enough and you need to put some functions on another 
monomer, especially for exchange and dispersion corrections, see e.g.

@ARTICLE{Williams:95b,
author="H. L. Williams and E. M. Mas and K. Szalewicz and B. Jeziorski",
journal=jcp,
volume=103,
pages=7374,
year=1995,
title="On the effectiveness of monomer-, dimer-, and bond-centered basis 
functions in the calculations
of the intermolecular interaction energy"
}

If you use molpro2008.1 and want to check how the MC+BS approach works for 
e.g. the electrostatic energy, you can look at testjobs/mcbs_inte.test.

Best wishes,

Tatiana

  On Thu, 26 Mar 2009, cong.wang wrote:

> Dear everyone,
>
> Hello!
>
> According to the manual of molpro, an example input for SAPT calculation is
>
> r=5.6
> geometry={nosym; he1; he2,he1,r}
> basis=avqz
>
> !wf records
> ca=2101.2
> cb=2102.2
>
> !monomer A
> dummy,he2
> {hf; save,$ca}
> sapt;monomerA
>
> !monomer B
> dummy,he1
> {hf; start,atdens; save,$cb}
> sapt;monomerB
>
> !interaction contributions
> sapt;intermol,ca=$ca,cb=$cb
> *******************************************
>
> My question is, since SAPT is BSSE free, why there is a "dummy" in the
> input file? If I omit the "dummy" in the input, the problem is error
> terminated.
>
> Thank you very much and best regards
> Cong Wang
>
> Ph.D. student
> Department of Chemistry
> Laboratory for Instruction in Swedish
> University of Helsinki
> A.I. Virtanens plats 1
> P.O. Box 55
> FI-00014 University of Helsinki
> FINLAND
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>

Dr. Tatiana Korona http://tiger.chem.uw.edu.pl/staff/tania/index.html
Quantum Chemistry Laboratory
University of Warsaw
Pasteura 1, PL-02-093 Warsaw, POLAND


`The man who makes no mistakes does not usually make anything.'
                                        Edward John Phelps (1822-1900)