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506. AMPAC: Austin Method 1 Package (Version 2.1)
by Dewar Research Group, Chemistry Department,
University of Texas, Austin, Texas 78712
AMPAC represents the current culmination of a project
that has occupied the Dewar group for twenty years and
which still continues, i.e., the development of quantum
mechanical procedures accurate enough, and simple
enough, to serve as a practical tool for chemists to
use in their own research. For a brief history, see
Ref. 1. Many contributed to the development of the
underlying theoretical procedures and their application
to a wide variety of chemical properties and to the
development of corresponding computer programs.
A few years ago, one of us (J.J.P.S.), as a member of
the Dewar Research Group, undertook the task of
rewriting and reorganizing these programs into a single
package, a project which also led to a major increase
in their efficiency, addition of further options, and
greatly simplified input. This package (MOPAC)2 has
gained wide acceptance.
Recently, we have developed3 a "third-generation"
treatment which seems to represent a major advance over
MINDO/3 or MNDO. Because of the continued confusion of
our procedures with other much inferior semiempirical
methods, we decided on a change from the previous "NDO"
nomenclature. The new treatment was therefore termed
AM1 (Austin Model 1). The name of the present package
has been changed correspondingly to AMPAC. It
represents an enhanced version of MOPAC, including AM1.
MINDO/3 and MNDO are retained, for completeness,
because there are areas where each is particularly
effective and because MNDO parameters are currently
available for a much wider range of elements than for
AM1.
A full configuration interaction treatment had been
developed earlier.4 This was inadvertently omitted
from MOPAC, where only C.I. options were available.
Full C.I. is now included in AMPAC.
The MNDO Hamiltonian has been extended to include d
orbitals, and preliminary parameters are included for
chromium. It should be stressed that these are
preliminary; our hope is that their use by others may
help to show up their deficiencies. We know already
that they perform poorly for p complexes.
MNDO parameters are now included for H, Be, B, C, N, O,
F, Hg, Al, Si, Ge, Sn, Pb, P, S, Cl, Br, and I. AM1
parameters are currently available for C, H, O, N, F,
Cl, Br, and I.
While MINDO/3 and MNDO had previously been extended to
linear polymers,5 no option for such calculations was
included in MOPAC. An improved treatment, applicable
to all three Hamiltonians, is included in AMPAC (it
represents a subset of MOSOL6).
A number of other minor additions and modifications are
documented in the AMPAC manual (Appendix D).
References:
- M.J.S. Dewar, J. Mol. Struct., 100, 41 (1985).
- J.J.P. Stewart, QCPE Bull., 3, 43 (1983).
- M.J.S. Dewar, E. G. Zoebisch, E. F. Healy, and J.J.P. Stewart, J. Am. Chem. Soc., 107, 3902 (1985).
- M.J.S. Dewar and C. J. Doubleday, J. Am. Chem. Soc., 100, 4935, (1978).
- M.J.S. Dewar, Y. Yamaguchi, S. H. Suck, Chem. Phys. Lett., 50, 259 (1977) and Chem. Phys., 43, 145 (1979).
- J.J.P. Stewart, QCPE Bull., 5, 62 (1985).
FORTRAN 77 (VAX)
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