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2 Polish Journal of Chemistry

2 1998

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On the chemical potential/electronegativity equalization in density functional theory

100%

Nalewajski R. F.

tom Vol. 72, nr 7S

1763-1778

General variational principles of the Kohn-Sham (KS) density functional theory are interpreted as the corresponding chemical potential/electronegativity equalization equations. The unconstrained (ground-state) and constrained (excited) electron configuratons are examined for both the system global description and for the case of its partitioning into mutually closed subsystems, e.g., reactants. The chemical potential discontinuity for the integer numbers of electrons at zero temperature is stressed, and the KS orbital description of he charge transfer (CT) between reactants is discussed. Using the appropriate ensemble formulation of the KS theory thein situ chemical potential/electronegativity difference, the driving 'force' behind the inter-reactant CT, is linked to the relevant KS frontier eigenvalues of polarized reactants.

Exploring bonding patterns of molecular systems using quantum mechanical bond multiplicities

51%

Mrozek J. , Nalewajski R. F. , Michalak A.

tom Vol. 72, nr 7S

1779-1791

One of the fundamental chemical concepts, the structural formula of a chemical species, which visualizes bonding patterns in a given molecular system, can also given a more flexible and quantified form in terms of alternative quantum-mechanical measures of bond-orders. The recently developed difference approach, based upon the one-determinantal wavefunction [Hartree-Fock(HF) and Kohn-Sham (KS) theories], compares the charge-and-bond-order matrix in a molecule (P) and that in the separated atoms limit (P(0), SAL) defined in the orthogonal basis set of atomic functions. In this approach the atomic and diatomic contibutions to the molecularly averaged difference between these matrices, /2 = 1/2tr[P(P(0) - P)], are used to define bond multiplicities. THe main purpose of this work is to examine the overall performance of such KS and HF bonding indices, when applied to the set of chemically well defined reference systems, and to use them to investigate bond-orders in more challenging molecules, which have recently been the subject of independent studies. Manifestations of changing bond ionicity by these effective bond-orders are examined for a series of diatomics. Some methodological aspects associated with alternative SAL choices are discussed and tested.