The SCF Total Electronic Energy

To obtain the total (electronic plus nuclear) energy, we add the internuclear repulsion energy for the N nuclei  

A great deal of research effort has gone into devising and comparing basis sets for ab initio calculations. There are essentially two important criteria  

We want a basis set that is capable of describing the actual wavefunction weU enough to give chemically useful results. 

We want a basis set that leads to integrals Fjj and Sij that we can evaluate reasonably accurately and quickly on a computer. 

Many types of basis set have been examined and two of these have come to dominate the area of ab initio molecular calculations. These two, which we refer to as the gaussian and the Slater-type-orbital (STO) basis sets, are actually very similar in many important respects. 

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