  A novel Rayleigh-Schr\"odinger many-body perturbation theory (MBPT) approach
is introduced by making use of a particle-number-breaking Bogoliubov reference
state to tackle (near-)degenerate open-shell fermionic systems. By choosing a
reference state that solves the Hartree-Fock-Bogoliubov variational problem,
the approach reduces to the well-tested M{\o}ller-Plesset, i.e., Hartree-Fock
based, MBPT when applied to closed-shell systems. Due to its algorithmic
simplicity, the newly developed framework provides a computationally simple yet
accurate alternative to state-of-the-art non-perturbative many-body approaches.
At the price of working in the quasi-particle basis associated with a
single-particle basis of sufficient size, the computational scaling of the
method is independent of the particle number. This paper presents the first
realistic applications of the method ranging from the oxygen to the nickel
isotopic chains on the basis of a modern nuclear Hamiltonian derived from
chiral effective field theory.
