We have computed accurate potential energy curves of the ground states of the PO(X (2)Pi), PO+(X (1)Sigma(+)) and PO-(X (3)Sigma(-)) species by multireference configuration interaction and coupled-cluster methods and have obtained accurate spectroscopic constants for each species. We have also determined the effect of core on the properties above and have obtained the PO complete basis set limit by the multireference method for the equilibrium energy, bond distance, dissociation energy, harmonic frequency, and dipole moment. (C) 2003 American Institute of Physics.