We consider a new formulation of the stochastic coupled cluster method in terms of the similarity transformed Hamiltonian. We show that improvement in the granularity with which the wavefunction is represented results in a reduction in the critical population required to correctly sample the wavefunction for a range of systems and excitation levels and hence leads to a substantial reduction in the computational cost. This development has the potential to substantially extend the range of the method, enabling it to be used to treat larger systems with excitation levels not easily accessible with conventional deterministic methods.
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This was generated for minimal debugging purposes and has geometry rLiH1 = 1 Å, rLiH2 = 1.1 Å, and θHLiH = 90°. In the STO-3G basis, unrestricted orbitals were prepared with a custom density functional with purely exchange, Ex = 2K + XSlater + XBecke88. Two core electrons and 8 virtual spinorbitals were frozen leaving an active space of 2 electrons in 4 spin orbitals. Q-Chem outputs and molecular orbital integrals for this system are included in the data repository.20