Austin Model 1, or AM1, is a
semi-empirical method for the
quantum
In physics, a quantum (: quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a property can be "quantized" is referred to as "the hypothesis of quantization". This me ...
calculation of molecular electronic structure in
computational chemistry
Computational chemistry is a branch of chemistry that uses computer simulations to assist in solving chemical problems. It uses methods of theoretical chemistry incorporated into computer programs to calculate the structures and properties of mol ...
. It is based on the
Neglect of Differential Diatomic Overlap integral approximation. Specifically, it is a generalization of the
modified neglect of differential diatomic overlap approximation.
Related methods are
PM3 and the older
MINDO
MINDO, or Modified Intermediate Neglect of Differential Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Intermediate Neglect of Differential Overlap ...
.
AM1 was developed by
Michael Dewar and co-workers and published in 1985. AM1 is an attempt to improve the
MNDO MNDO, or Modified Neglect of Diatomic Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Diatomic Differential Overlap integral approximation. ...
model by reducing the repulsion of atoms at close separation distances. The atomic core-atomic core terms in the MNDO equations were modified through the addition of off-center attractive and repulsive
Gaussian functions.
The complexity of the parameterization problem increased in AM1 as the number of parameters per atom increased from 7 in
MNDO MNDO, or Modified Neglect of Diatomic Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Diatomic Differential Overlap integral approximation. ...
to 13-16 per atom in AM1.
The results of AM1 calculations are sometimes used as the starting points for parameterizations of forcefields in
molecular modelling
Molecular modelling encompasses all methods, theoretical and computational, used to model or mimic the behaviour of molecules. The methods are used in the fields of computational chemistry, drug design, computational biology and materials scien ...
.
AM1 is implemented in the
MOPAC
MOPAC is a computational chemistry software package that implements a variety of semi-empirical quantum chemistry methods based on the neglect of diatomic differential overlap (NDDO) approximation and fit primarily for gas-phase thermochemistry ...
,
AMPAC,
Gaussian,
CP2K
CP2K is a freely available ( GPL) quantum chemistry and solid state physics program package, written in Fortran 2008, to perform atomistic simulations of solid state, liquid, molecular, periodic, material, crystal, and biological systems. It prov ...
,
GAMESS (US)
General Atomic and Molecular Electronic Structure System (GAMESS (US)) is computer software for computational chemistry. The original code started on October 1, 1977 as a National Resources for Computations in Chemistry project. In 1981, the code ...
,
PC GAMESS,
GAMESS (UK), and
SPARTAN programs.
An extension of AM1 is
SemiChem Austin Model 1 (SAM1), which is implemented in the
AMPAC program and which explicitly treats d-orbitals.
An extension of AM1 is
AM1* that is available in
VAMP software.
See also
*
Semi-empirical quantum chemistry method
Semi-empirical quantum chemistry methods are based on the Hartree–Fock formalism, but make many approximations and obtain some parameters from empirical data. They are very important in computational chemistry for treating large molecules where t ...
s
Notes
References
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Semiempirical quantum chemistry methods
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