Subject: Question: the nuclear-nuclear interaction in MOPAC

From: Taisung Lee <[email-masked]>
Date: Mon, 5 Jan 1998 14:56:54 -0500 (EST)

Hi Everyone,

    I got a question about  the nuclear-nuclear interaction in MOPAC
program.  I couldn't find Dr. James Stewart's email address.  If anyone
here can answer my question or forward Dr. Stewart's email address to me,
I really appreciate.

    I found in the MOPAC93 R2 manual p115, the core-core term in MNDO for
NH/OH pair is in the form of 

    Eab=ZaZb<SaSa|SbSb>(1 + exp( -Rab*Ab) / Rab + exp( -Rab*Aa) )--(1)

    while in the MOPAC program (subroutine rotate.f) and in the orginal
MNDO paper (JACS 99 4899 (1977)) this term is in the form of

    Eab=ZaZb<SaSa|SbSb>(1 + exp( -Rab*Ab) * Rab + exp( -Rab*Aa) )--(2)

    They give quite different answers.  Could anyone tell me which is the
correct one?

    Thanks in advance.

Taisung Lee
Research Associate 
Department of Chemistry
Duke University
[email-masked]