ISSN:
0020-7608
Keywords:
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
We provide a numerical test of a new approach to calculating approximate interatomic interaction energies based on partial antisymmetry (PA) [Adams, Chem. Phys. Lett. 68, 511 (1979)]. We use spin-coupled products of single determinant atomic wave functions to approximate a particular primitive wave function of the diatomic. Three methods are used: (1) the conventional full antisymmetry (FA) approach, in which the primitive wave function is antisymmetrized and the difference of expectation values of the total energies of the diatomic and atomic systems is calculated, (2) the PA approach, in which only some of the terms of the antisymmetrizer are applied to the primitive wave function, and the energy expressions are simplified based on approximations to the PA theorem [Adams, op. cit.], and (3) a hybrid approach based on a combination of assumptions from the first two approaches, which is comparable to the work of Dacre and McWeeny [Proc. Roy. Soc. London A317, 435 (1970)]. Results are compared with accurate potential curves from the literature. Interaction energies were calculated for the X 1Σ+g states of Ne2, Li2, and Na2, the X 1Σ+ states of LiNa and LiF, the x 3Σ+u states of Li2 and Na2, x 7Σ+u, and x 3Σ+ LiNa at several internuclear distances. In all cases but Ne2, the PA and FA interaction energies are much closer to each other than is either to the accurate reference values. In these cases there is thus no significant penalty exacted for the use of PA over FA, even though it is easier to use. By conventional reasoning, neither the PA nor the Dacre-McWeeny approaches should work at short range or for binding molecules, because they truncate expansions of the antisymmetrizer in the energy expression. Our results provide counter examples to change that expectation, thus providing additional evidence in support of an approximate approach based on the PA theorem.
Additional Material:
1 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/qua.560382474
Permalink
