  Convergence aspects of nuclear many-body perturbation theory for ground
states of closed-shell nuclei are explored using a Brillouin-Wigner formulation
with a new vertex function enabling high-order calculations. A general
formalism for Hamiltonian partitioning and a convergence criterion for the
perturbation series are proposed. Analytical derivation shows that with optimal
partitionings, the convergence criterion for ground states can always be
satisfied. This feature attributes to the variational principle and does not
depend on the choice of an internucleon interaction or a many-body basis.
Numerical calculations of the ground state energies of 4He and 16O with
Daejeon16 and a bare N3LO potential in both harmonic-oscillator and
Hartree-Fock bases confirm this finding.
