Subject: Overlap between MO of 2 molecules

From: "Petr Toman" <[email-masked]>
Date: Thu, 29 Jun 2000 16:42:05 +0200

Dear colleagues,
Could somebody give me an advice how could I calculate the overlap between 
molecular orbitals of 2 neighbouring molecules (preferably by Gaussian)? 
1)
Would it be correct to calculate firstly the MO of each molecule by itself 
to obtain the molecular orbital coefficients C_mi, then perform the 
calculation of both molecules together to obtain the overlap matrix 
(between AO) S_mn.
Finally compute the overlap between i-th MO of the first molecule and j-th 
MO of the second molecule as
  SUM    (C_mi * C_nj * S_mn) 
over m,n

where m are the AO of the 1. molecule and n are the AO of the 2. molecule.

2)
By the way, how could I force Gaussian 98 to print overlap matrix ???

3)
What method could be reliable (B3LYP, HF,...)?

Thanks a lot,

Petr