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Politzer P.,CleveTheoComp LLC | Peralta-Inga Shields Z.,CleveTheoComp LLC | Bulat F.A.,Fable Theory and Computation LLC | Murray J.S.,CleveTheoComp LLC
Journal of Chemical Theory and Computation | Year: 2011

Historically, two important approaches to the concept of electronegativity have been in terms of: (a) an atom in a molecule (e.g., Pauling) and (b) the chemical potential. An approximate form of the latter is now widely used for this purpose, although it includes a number of deviations from chemical experience. More recently, Allen introduced an atomic electronegativity scale based upon the spectroscopic average ionization energies of the valence electrons. This has gained considerable acceptance. However it does not take into account the interpenetration of valence and low-lying subshells, and it also involves some ambiguity in enumerating d valence electrons. In this paper, we analyze and characterize a formulation of relative atomic electronegativities that is conceptually the same as Allen's but avoids the aforementioned problems. It involves the property known as the average local ionization energy, Ī(r), defined as Ī(r)=Σρi(r)|εi|ρ(r), where ρi(r) is the electronic density of the ith orbital, having energy εi, and ρ(r) is the total electronic density. Ī(r) is interpreted as the average energy required to remove an electron at the point r. When Ī(r) is averaged over the outer surfaces of atoms, taken to be the 0.001 au contours of their electronic densities, a chemically meaningful scale of relative atomic electronegativities is obtained. Since the summation giving Ī(r) is over all occupied orbitals, the issues of subshell interpenetration and enumeration of valence electrons do not arise. The procedure is purely computational, and all of the atoms are treated in the same straightforward manner. The results of several different Hartree-Fock and density functional methods are compared and evaluated; those produced by the Perdew-Burke-Ernzerhof functional are chemically the most realistic. © 2011 American Chemical Society. Source


Bulat F.A.,Fable Theory and Computation LLC | Burgess J.S.,Fable Theory and Computation LLC | Burgess J.S.,U.S. Navy | Matis B.R.,Fable Theory and Computation LLC | And 5 more authors.
Journal of Physical Chemistry A | Year: 2012

We have investigated the use of the average local ionization energy, Ī s(r), as a means for rapidly predicting the relative reactivities of different sites on two model graphene surfaces toward the successive addition of one, two, and three hydrogen or fluorine atoms. The Ī s(r) results were compared with directly computed interaction energies, at the B3LYP/ 6-311G(d,p) level. Ī s(r) correctly predicts that the edges of graphene sheets are more reactive than the interior portions. It shows that added hydrogens activate the adjoining (ortho) sites and deactivate those that are separated by one site (meta). Overall, Ī s(r) is effective for rapidly (single calculations) estimating the relative site reactivities of these large systems, although it reflects only the system prior to an interaction and cannot take into account postinteraction factors, e.g., structural distortion. © 2012 American Chemical Society. Source

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