Quantitative structure-property total interaction energy

Almost all applications of quantum mechanics to the problem of quantitatively describing molecular electronic structure begin with the choice of a suitable basis set in terms of which the electronic wavefunction is then parametrized. This choice of basis set is crucial, since it ultimately determines the accuracy of the calculation, whether it be a matrix Hartree-Fock calculation, a conflguration-interaction study or a many-body perturbation theory expansion, whether it is a calculation of the total energy of a system, the energy of interaction between two subsystems, or the determination of some electric or magnetic property. 

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