ELSEV IER THEO CHEM Journal of Molecular Structure (Theochem) 394 (1997) 19-23 Computing electron affinities of radicals functional theory methods Branko S. Jursic with density zyxwvutsrqponmlkjihgfedc Department of Chemistp. Universir?: of‘ NW Orleans, New Orleuns, L4 70148. USA Received 20 August 1996; accepted I5 October 1996 Abstract A systematic computational study of the electron affinities for methyl, methoxy, and nitrile radicals with 24 density func- tional theory methods is presented. The computation is performed using the immense 6-3 I I + + G(3df,3pd) Gaussian basis set. The computed values are compared with the experimental results and the DFT methods which accurately predict the electron affinities are selected. 0 1997 Elsevier Science B.V. Keywords: Radicals; Electron affinity; DFT 1. Introduction The computation of chemical and physical proper- ties of interest has been a goal of chemists for a long time. There are many different computational meth- ods that have been used for these purposes (for exam- ple, see a series of books edited by Lopkowitz and Boyed [ 11). The size of the studied molecule is crucial when selecting a computational method. Three widely known groups of computational methods: molecular mechanics, semiempirical, and ab initio methods are currently used [2]. The accuracy of the molecular mechanics and semiempirical methods depends on how well they are parametrized. In many cases researchers have considerable problems generating reliable parameters. On the other hand, ab initio meth- ods do not require parameters but are computationally expensive and consequently applicable only to small molecular systems [3]. If very accurate computational results are required then the even more expensive ab initio electron correlation methods are needed. The application of Density Functional Theory (DFT) to chemical systems is relatively recent [4]. Although scientists realized early that chemical prop- erties can be explained by electron density changes, it was only two decades ago that it became possible to solve mathematical equations by using orbitals to represent electron density [5]. Because of approxima- tions in solving the mathematical equations for DFT methods there is no logical improvement in Dm methods over ab initio methods. For example, includ- ing a higher level of electron correlation and a larger basis set should ultimately lead to a computational result close to that obtained by solving the Schrodinger equation [3]. This pitfall of DFT methods can be eliminated only through the systema- tic evaluation of the molecular systems for which experimental data are available. Thus we have studied geometries, activation barriers [6], heat of reactions [7], bond dissociation energies [ 81, ionization poten- tials [9], and heats of formation for many chemical reactions [lo]. Here we present systematic studies of 0 166.1280/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved P/I SOl66-1280(96)04914-7