A Hylleraas functional based perturbative technique to relax the extremely localized molecular orbital wavefunction

A way to reduce the computational cost associated with the study of large molecules exploits the transfer of extremely localized molecular orbitals (ELMOs). Unfortunately, due to the reduction in the number of variational parameters, the ELMO description is not as accurate as the Hartree-Fock one, although it is qualitatively correct in most of the cases. Therefore, in order to overcome this significant drawback, we propose a perturbative ELMO approach exploiting the Hylleraas functional. Preliminary tests have been performed and the results are promising for future applications to large systems. (C) 2008 American Institute of Physics.