Monte Carlo methods in electronic structures for large systems

Quantum Monte Carlo methods have recently made it possible to calculate the electronic structure of relatively large molecular systems with very high accuracy. These large systems range from positron complexes [NH2,Ps] with N IO electrons to C-20 isomers with 120 electrons, to silicon crystal structu res of 250 atoms and 1000 valence electrons. The techniques for such calcul ations and a sampling of applications are reviewed.