Subject: Questions of MOPAC

From: Tianying Yan <[email-masked]>
Date: Sun, 4 Aug 2002 23:13:51 -0400 (EDT)

Deal cclers,

I am a Ph.D. student in computational chemistry and am new in using
semi-empirical package MOPAC version 7.0. Here I have several questions
and hopefully get help from experts like you:

1. In MOPAC7.0, is there a rigid scan method, just doing the same work as
the 'scan' keywork in Gaussian 9x, for scanning the PES of A + B
interactions? or is there any other alternative way to do it? It is too
tedious to change the input .dat file every time for every single point
calculations.

2. If I want to evaluate A + B vdW interaction at certain A-B distant as
well as configuration using MOPAC7.0, is the following equation correct?

  E(A-B vdW) = Escf(A-B) - Escf(A) - Escf(B)

Also, is there any correction to account for basis set superposition
error (BSSE) in MOPAC 7.0?

3. If I want to use MOPAC to evaluate reaction energy, A + B -> C + D, is
the following equation correct?

  Reaction Energy = Escf(C) + Escf(D) - Escf(A) - Escf(B)
                  +  ZPE(C) +  ZPE(D) -  ZPE(A) -  ZPE(B)

4. As indicated in MOPAC 7.0 Manual, "Escf (defined as Heat of formation),
force constants and normal mode vibrations are all related to the values
at 25 degree C." (cited directly from the Manual), the above values in Q.2
and Q.3 (supposed it is correct) are related to 25 degree C. Here comes
another question, is there any convienent way to convert them to 0 or any
other degree in Kelvin?

In above questions, I implicitly consider using PM3 method, while I
believe these questions can be also applied to other semi-empirical
methods (MNDO, MINDO/3 and AM1) included in MOPAC7.0. Any suggestion will
be much more than welcome!

Regards, Tianying

Tianying Yan
Institute for scientific computing
Department of Chemistry
Wayne State University
Detroit, MI 48202