The approximate coupled cluster singles and doubles model (CC2) has been proven to be a valuable quantum chemistry approach that is widely used to calculate ground-state and excited-state properties for molecular systems. However, CC2 theory suffers from high computational expense, where the computational cost scales as O(N5) with system size (N is number of electrons). Here, we introduce a stochastic resolution of identity approximation (sRI) to CC2 approach, which allows us to reduce the scaling from O(N5) to O(N3). We benchmark our sRI-CC2 approach for hydrogen dimer chains. We show that sRI-CC2 agrees with RI-CC2 approach for ground state energy within stochastic error bar. We demonstrate that the overall computational scaling of our sRI-CC2 is indeed close to O(N3). Further work must study sRI-CC2 approach for excitation energies.

Stochastic resolution of identity to CC2 ground-state energy for large systems

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