Equation-of-motion coupled-cluster method with double electron-attaching operators: Theory, implementation, and benchmarks

S. Gulania, E. F. Kjonstad, J. F. Stanton, H. Koch, and A. I. Krylov
J. Chem. Phys. , submitted (2021)

We report a production-level implementation of equation-of-motion coupled-cluster method with double electron-attaching EOM operators of 2p and 3p1h types, EOM-DEA-CCSD. This ansatz, suitable for treating electronic structure patterns that can be described as two-electrons-in-many orbitals, represents a useful addition to EOM-CC family of methods. We analyze the performance of EOM-DEA-CCSD for energy differences and molecular properties. By considering reduced quantities, such as state and transition one-particle density matrices, we can compare EOM-DEA-CCSD wave functions with wave functions computed by other EOM-CCSD methods. The benchmarks illustrate that EOM-DEA-CCSD is capable of treating diradicals, bond-breaking, and some types of conical intersections.

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