Multireference explicitly correlated F12 theories

Abstract

We review our recent developments in multireference explicitly correlated F12 theories (explicitly correlated internally contracted multireference perturbation and multireference configuration interaction theories) that achieve near-basis-set-limit accuracy of the underlying multireference electron correlation methods with basis sets of medium size. The applicability of the multireference F12 theories is the same as that of their non-F12 counterpart, and therefore it is a computational tool with predictive accuracy for complicated electronic structures with strong correlation. A comparison with the earlier developments by others is also discussed.

Keywords:

• multireference methods
• multireference configuration interaction
• MRCI
• multireference perturbation theory
• CASPT2
• explicit correlation
• F12
• internal contraction

Acknowledgements

The authors thank Dr Kodagenahalli R. Shamasundar for a kind help on the Cr₂ calculations. This work has been supported by the Deutsche Forschungsgemeinschaft as part of an DFG-NSF project and by the Fonds der Chemischen Industrie. T.S. is supported by the Japan Society for the Promotion of Science Research Fellowship for Research Abroad.

Notes

^aThe CABS singles corrections (CI) are included.

^aF12 calculations for the aV6Z basis were not performed since there are no fitting and CABS basis sets.