The --electron approximation

We therefore start the quantum mechanical treatment of conjugated systems by expressing the total electronic wavefunction in terms of a wave function for the cr-electrons and a wavefunction for the 97-electrons  

Hi and Hi refer respectively to a and 77-electrons exclusively and the Hamiltonian Hw can also be written as 

These last two equations have the same form as eqns (10-2.1) and 

Within the framework of the 77-electron approximation Ea is assumed to be simply a constant and the expression for Ew is used to find the optimum 77-electron LCAO MOs, that is, the Hartree-Fock-Roothaan 

Our approximations so far (the orbital approximation, LCAO MO approximation, 77-electron approximation) have led us to a tt-electronic wavefunction composed of LCAO MOs which, in turn, are composed of 77-electron atomic orbitals. We still, however, have to solve the Hartree-Fock-Roothaan equations in order to find the orbital energies and coefficients in the MOs and this requires the calculation of integrals like (cf. eqns (10-3.3))  

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The electronic approximation switch NAHE was especially developed for devices at which it is necessary to start an electrical equipment without touching. The sensor is based on the opto-electronic principle. The beam of a transmitter is reflected diffusely on a target (e.g. hands) and registered by a receiver. The switching distance of 140... 190 mm can be adjusted according io customer s specification The switching on load ls S A/230 VAC or 1 A/l20 VAC. 

The study of the reactivity of the nucleic acid bases utilizes indices based on the knowledge of the molecular electronic structure. There are two possible approaches to the prediction of the chemical properties of a molecule, the isolated and reacting-molecule models (or static and dynamic ones, respectively). Frequently, at least in the older publications, the chemical reactivity indices for heteroaromatic compounds were calculated in the -electron approximation, but in principle there is no difficulty to define similar quantities in the all-valence or allelectron methods. The subject is a very broad one, and we shall here mention only a new approach to chemical reactivity based on non-empirical calculations, namely the so-called molecular isopotential maps. 

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