# Off-diagonal elements of the CI matrix

Dear CCL readers,
I am writing a program to do CI calculations on some conjugated
molecules using semiempirical (PPP) parameters. Unfortunately, I am having
problems to calculate the off-diagonal elements of the CI matrix. In their book
Szabo e Ostlund show (tables 2.3 and 2.4) how to calculate these elements when
the determinants are in maximum coincidence. I am looking for references where
I
can find the answer to the following simple(?) question:
HOW TO CALCULATE THE NUMBER OF PERMUTATIONS NECESSARY TO OBTAIN MAXIMUM
COINCIDENCE BETWEEN THE DETERMINANTS?
In other words:
WHEN SHOULD I MULTIPLY THE EQUATIONS SHOWN IN THE BOOK BY -1?
Thank you very much in advance. I will sumarize.
Sincerely yours,
Gustavo L.C. Moura
gustavo -8 at 8- hathi.chem.pitt.edu