Electron affinity evaluation

Table 2.2 Comparison of W2 and W1 theories, and their variants for the evaluation of electron affinity and ionization potential (eV) for selected species from G2-1 test set.

The determination of electron affinities (EAs) is one of the most serious problems in quantum chemistry. While the Hartree-Fock electron affinity can be easily evaluated, most anions turn out to be unbound at this level of theory. Thus, the correlation effects are extremely crucial in evaluating EAs. At this point, lithium hydride and lithium hydride anion make up a very good benchmark system because they are still small enough yet exhibit features of more complicated systems. Four and five electrons, respectively, give rise to higher-order correlation effects that are not possible in H2. 

The work function of the rubbing surfaces and the electron affinity of additives are interconnected on the molecular level. This mechanism has been discussed in terms of tribopolymerization models as a general approach to boundary lubrication (Kajdas 1994, 2001). To evaluate the validity of the anion-radical mechanism, two metal systems were investigated, a hard steel ball on a softer steel plate and a hard ball on an aluminum plate. Both metal plates emit electrons under friction, but aluminum produced more exoelectrons than steel. With aluminum, the addition of 1% styrene to the hexadecane lubricating fluid reduced the wear volume of the plate by over 65%. This effect considerably predominates that of steel on steel. Friction initiates polymerization of styrene, and this polymer formation was proven. It was also found that lauryl methacrylate, diallyl phthalate, and vinyl acetate reduced wear in an aluminum pin-on-disc test by 60-80% (Kajdas 1994). 

A substantial body of data exists evaluating the utility of DFT (and other methods) for computing ionization potentials and electron affinities following a ASCF approach. These data are summarized over four different test sets in Table 8.4. The conclusions one may... 

The simplest method for calculating the ionization potentials and the electron affinities is the 7T-HMO method. Such an evaluation is particularly suitable for the determination of the relative electron donor-acceptor properties of the molecules. The appropriate indices are the energies of the highest occupied molecular orbitals (HOMO) for the electron donor capacity and the energies of the lowest empty molecular orbitals (LEMO) for the electron acceptor abilities. These simple theoretical predictions gave an excellent interpretation1,256 of the... 

The parameter a is evaluated from valence state ionization potentials Ii and electron affinity At in the same valence state. Two distinct cases may arise ... 

The initial Hiickel calculations can be employed to obtain preliminary values for the electron densities and bond orders, from which the self-consistent field matrix elements can be evaluated by introduction of the chosen core potentials and electron repulsion integrals.11 Table I lists the ionization potentials, electron affinities and nuclear charges employed in the present calculations. 

It might be of interest to investigate the reactivity of additional functional groups by examining organic cyanates, thiocyanates, selen-ides, tellurides, phosphines, arsenides and others. All these compounds, which are expected to be reactive towards e q, await investigation that may help to evaluate their electron affinities. 

The free electron interacts with all atoms and molecules that have finite electron affinities to produce anions, and thus is unstable in all except the most inert liquids. Electrochemistry attests to this general axiom and provides a convenient means for evaluation of the energetics for the addition of an electron to solvent molecules and to species at the electrode-solution interface, for example ... 

We will investigate the stability of the anionic lithium clusters in Section 5. A relevant quantity is the dependence of the binding energy per atom on the number of atoms, as well as the electron affinity of neutral Lin clusters. From the latter, we evaluate whether these neutral clusters are able to receive an extra electron and to form an anionic system. 

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