Sub-system quantum dynamics using coupled cluster downfolding techniques

Understand

In this paper, we discuss extending the sub-system embedding sub-algebra coupled cluster (SESCC) formalism and the double unitary coupled cluster (DUCC) Ansatz to the time domain.

• An important part of the analysis is associated with proving the exactness of the DUCC Ansatz based on the general many-body form of anti-Hermitian cluster operators defining external and internal excitations.
• Using these formalisms, it is possible to calculate the energy of the entire system as an eigenvalue of downfolded/effective Hamiltonian in the active space, that is identifiable with the sub-system of the composite system.
• It can also be shown that downfolded Hamiltonians integrate out Fermionic degrees of freedom that do not correspond to the physics encapsulated by the active space.