Internally contracted multi-reference configuration interaction (MRCI) and coupled cluster singles doubles and perturbative triples [CCSD(T)] 26 correlated wavefunction theory (WFT) calculations were carried out with the MOLPRO 2015.1 code. These calculations used the largest Abelian subgroup, C2v, of the parent C∞v point group associated with the linear species HfCX (X = O, S, Se, Te, Po).