  We study the ground and low-lying excited states of O-15, O-17, N-15, and
F-17 using modern two-body nucleon-nucleon interactions and the suitably
designed variants of the ab initio equation-of-motion coupled-cluster theory
aimed at an accurate description of systems with valence particles and holes. A
number of properties of O-15, O-17, N-15, and F-17, including ways the energies
of ground and excited states of valence systems around O-16 change as functions
of the number of nucleons, are correctly reproduced by the equation-of-motion
coupled-cluster calculations. Within a harmonic oscillator basis and large
effective model spaces, our results are converged for the chosen two-body
Hamiltonians. Thus, all disagreements with experiment are, most likely, due to
the degrees of freedom such as three-body interactions not accounted for in our
effective two-body Hamiltonians. In particular, the calculated binding energies
of O-15/N-15 and O-17/F-17 enable us to rationalize the discrepancy between the
experimental and recently published [Phys. Rev. Lett. 94, 212501 (2005)]
equation-of-motion coupled-cluster excitation energies for the Jpi=3- state of
O-16. The results demonstrate the feasibility of the equation-of-motion
coupled-cluster methods to deal with valence systems around closed-shell nuclei
and to provide precise results for systems beyond A=16.
