Basis set reduction in Hilbert space.
We present Hilbert-space basis set reduction as a novel approach to reduce the computational effort of accurate correlation calculations for large basis sets. We motivate the method by an examination of the perturbative corrections in scaling theory and present a criterion for the choice of the internal basis. The method is illustrated with two calculations for the ground state of carbon and the energy curve of the beryllium dimer. In either case the errors introduced are less than 1% of the correlation energy. The method scales as the second power of the number of the basis functions and can exploit the benefits of massive parallelization