SAM1, or "Semiempirical ab initio Model 1", is a
semiempirical
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 ...
quantum chemistry
Quantum chemistry, also called molecular quantum mechanics, is a branch of physical chemistry focused on the application of quantum mechanics to chemical systems, particularly towards the quantum-mechanical calculation of electronic contributions ...
method for computing molecular properties. It is an implementation the general Neglect of Differential Diatomic Overlap (NDDO) integral approximation, and is efficient and accurate. Related methods are
AM1,
PM3 and the older
MNDO.
SAM1 was developed by
M.J.S. Dewar and co-workers at the University of Texas and the University of Florida. Papers describing the implementation of the method and its results were published in 1993
[ ] and 1994.
The method is implemented in the
AMPAC program produced b
Semichem
SAM1 builds on the success of the Dewar-style semiempirical models by adding two new aspects to the AM1/PM3 formalism:
#Two-electron repulsion integrals (TERIs) are computed from a minimal basis set of contracted Gaussian functions, as opposed to the previously used multipole expansion. Note that the NDDO approximation is still in effect, and that only a few of the possible TERIs are explicitly computed. The values of the explicit TERIs are scaled using empirically-derived functions to obtain experimentally relevant results.
#One-center two-electron repulsion integrals (OCTEs) are derived initially to reproduce atomic properties. These values are then fixed and carried forward as further elemental parameterization proceeds.
The performance of SAM1 for C, H, O, N, F, Cl, Br, and I was claimed to be superior to other semiempirical methods.
Especially noteworthy were the smaller systematic errors for heats for formation.
.
See also
*
Semi-empirical quantum chemistry method
*
NDDO
References
Semiempirical quantum chemistry methods
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