Explicitly correlated renormalized second-order Green's function for accurate ionization potentials of closed-shell molecules

Abstract

We present an energy-dependent explicitly correlated (F12) formalism for the nondiagonal renormalized second-order (NR2) Green's function method of closed-shell molecules. For a test set of 21 small molecules, the mean basis set error in IP computed using NR2-F12 with aug-cc-pVTZ basis is 0.028 eV, compared to 0.044 eV for NR2 with aug-cc-pV5Z basis. Similarly, for a set of 24 medium-sized organic electron acceptor molecules (OAM24), the mean basis set errors are 0.015 eV for NR2-F12 with aug-cc-pVTZ basis compared to 0.067 eV for NR2 with aug-cc-pVQZ basis. Hence, NR2-F12 facilitates accurate calculation of IP at a lower cost compared to the NR2 method. NR2-F12 has O(N6)/O(N5) noniterative/iterative costs with system size. At a small basis, the performance of NR2-F12 for 21 small molecules and OAM24 dataset is comparable to equation-of-motion ionized coupled-cluster singles and doubles, whose cost is iterative O(N6).