CASCI reference wave functions for multireference perturbation theory built from Hartree-Fock or Kohn-Sham orbitals

The MRMP2 method and many similar variants of multireference perturbation theory have a potentially wide range of applicability. However they typically require a CASSCF calculation to define the reference wave function. It is worthwhile to investigate whether 'simpler' orbitals than those obtained from the full CASSCF procedure can provide useful accuracy. In this study we investigate six reactions taken from the Zhao-Gonzalez-Garcia-Truhlar database and investigate the MRMP2 procedure when used with a variety of different orbital sets in order to assess the reliability of such procedures. The results are encouraging and suggest that multireference perturbation theory may be used, for some systems, with the simplified procedures presented here.