Approximate density function

A Kuki, PG Wolynes. Electron tunneling paths in proteins. Science 236 1647-1652, 1987. T Ziegler. Approximate density functional theory as a practical tool m molecular energetics and dynamics. Chem Rev 91 651-667, 1991. 

Hertwig, R.H., Hrusak, J., Schroder, D., Koch, W. and Schwarz, H. (1995) The metal-ligand bond strengths in cationic gold(l) complexes. Application of approximate density functional theory. Chemical Physics Letters, 236, 194-200. 

Andzelm and Wimmer, 1992, published one of the first comprehensive studies on the performance of approximate density functional theory in which optimized molecular geometries were reported. These authors computed the geometries of several organic species containing the atoms C, N, O, H, and F at the local SVWN level, using a polarized double-zeta basis set optimized for LDA computations. Some trends have been discerned... 

What is obviously needed is a generally accepted recipe for how atomic states should be dealt with in approximate density functional theory and, indeed, a few empirical rules have been established in the past. Most importantly, due to the many ways atomic energies can be obtained, one should always explicitly specify how the calculations were performed to ensure reproducibility. From a technical point of view (after considerable discussions in the past among physicists) there is now a general consensus that open-shell atomic calculations should employ spin polarized densities, i. e. densities where not necessarily... 

It has been noted in Hay s paper that the occupations for the d1, d4, d6, and d9 states are in principle arbitrary. This does not strictly hold true for density functional applications because of the above-mentioned dependence of the energy on the shape of the occupied orbitals. The density generated from occupying the dz2 differs from the one obtained from placing the electron in, e. g the d orbital. Feeding an approximate density functional with these two unequal densities may lead to non-identical energies (cf. Figure 5-2). In most practical applications, however, the errors introduced in this way should be much smaller than those caused by other limitations of the functional or basis set employed. 

Ziegler, T., 1991, Approximate Density Functional Theory as a Practical Tool in Molecular Energetics and... 

Filippi, C., C. J. Umrigar, and M. Taut. 1994. Comparison of exact and approximate density functionals for an exactly soluble models. J. Chem. Phys. 100, 1290. 

Approximate density functional theory calculations have been used to investigate the irons influence in [Os(N)(X)4] (X = Cl, Me, SMe) and [Os(N)(Cl)5] ". By using the transition state method the relative effects of steric and electronic stabilization on the trans influence in these complexes have been quantitatively assessed. It is found that the electronic stabilization is greater than the steric stabilization for these complexes. 

In this review we will give an overview of the properties (asymptotics, shell-structure, bond midpoint peaks) of exact Kohn-Sham potentials in atomic and molecular systems. Reproduction of these properties is a much more severe test for approximate density functionals than the reproduction of global quantities such as energies. Moreover, as the local properties of the exchange-correlation potential such as the atomic shell structure and the molecular bond midpoint peaks are closely related to the behavior of the exchange-correlation hole in these shell and bond midpoint regions, one might be able to construct... 

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