LOCALIZED ORBITALS FOR MOLECULAR CALCULATIONS

We present an overview of the existing localization algorithms which h ave been of are being used to perform quantum chemical molecular calcu lations that take into account electronic correlation effects. The nat ural distinction between intrinsic and extrinsic localization methods is explained and developed. The advantages and drawbacks of specific m ethods are discussed in terms of CPU time required to obtain the (in m ost cases) almost identical localized molecular orbitals. Finally, we show using a specific example of a second order multireference perturb ational calculation, the enormous gain in computer time that the use o f localized molecular orbitals can bring. We also show explicitly the ''concentration'' of second order Moller-Plesset correlation energy in to a much smaller perturbed space.