Accurate Ab Initio Calculation of Ionization Potentials of the First-Row Transition Metals with the Configuration-Interaction Quantum Monte Carlo Technique

Accurate ionization potentials of the first-row transition-metal atoms are obtained via the initiator full configuration quantum Monte Carlo technique, performing a stochastic integration of the electronic Schrödinger equation in exponentially large Hilbert spaces, with a mean absolute error of 0.13 kcal/mol (5 meV). This accuracy requires correlation of the 3p semicore electrons and in some cases the 3s manifold, along with extrapolation of the correlation energies to the complete-basis-set limit, and provides a new theoretical benchmark for the ionization potentials of these systems.