Overlap between MO of 2 molecules

["Petr Toman" <toman (- at -) imc.cas.cz>]

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