Particle-particle and quasiparticle random phase approximations: connections to coupled cluster theory.

摘要: We establish a formal connection between the particle-particle (pp) random phase approximation (RPA) and ladder channel of coupled cluster doubles (CCD) equations. The relationship RPA CCD is best understood within Bogoliubov quasiparticle (qp) formalism. This work follow-up to our previous proof on particle-hole (ph) ring-CCD. Whereas quasibosonic approximation, CC theory “correct bosonization” in sense that wavefunction Hilbert space are exactly fermionic, yet amplitude equations can be interpreted as adding different channels together. Coupled achieves this goal by interacting ph (ring) pp (ladder) diagrams via third we here call “crossed-ring” whose presence allows for full fermionic antisymmetry. Additionally, incorporates what “mosaic” terms which absorbed into defining new effective one-body Hamiltonian. inclusion these mosaic seems quite important. pp-RPA qp-RPA textbook material nuclear structure physics but largely unknown quantum chemistry, where particle number fluctuations determinants rarely used. believe ideas connections discussed paper may help design improved ways incorporating correlation density functionals based perspective.