Subject: MOPAC 93 - reply regarding accuracy

From: [email-masked] (Dr. James Stewart)
Date: Sun, 4 Jul 93 08:04:46 PDT

>From Dave Ewing, John Carroll University:

>  We cannot reproduce some of the published results on a couple of transition
>  states using MINDO/3 and MNDO.  Our bond lengths agree but angles are off
>  by as much as 2 degrees and activation energies are off by nearly 1 Kcal/
>  mol.  The paper to which we are comparing was published in 1988.  Are the
>  standard parameters slightly different now (we're using MOPAC 93) such that
>  these differences would be expected?

The fundamental constants (e, h, c, etc.) in MOPAC 93 have been updated
at the suggestion of Dr Yoshihisa Inoue of The Green Cross Corp, Japan,
to conform with the CODATA standards.  This will cause small changes in
the results.  The parameters in the methods have not been changed.
See page 162 of the manual.  Updating the fundamental constants was long
overdue.  As the new constants are accurate to about one part per million,
I do not expect the next update of these constants to cause the results
to change noticeably.

Baker's EF routine has been improved by Dr Frank Jensen of Odense, Denmark,
so that now a much higher precision can be achieved.  See page 142 of the
manual.

Together these changes should account for the differences in the results
obtained from MOPAC 93 and earlier results.

James J. P. Stewart.