Relativistic, quantum electrodynamic and many-body effects in the water molecule

Ab initio calculations are reported of the electronic structure of the water molecule, based on the Dirac theory of the electron using correlation consistent basis sets. We calculate electron correlation corrections by second-order many-body perturbation theory, NMR shielding constants in the four-component relativistic interaction Hamiltonian formulation of QED, and report the first calculation of the electronic structure of a molecular system in which the Breit interaction is included both perturbatively and variationally in the calculation of the total energy.