It was recalled that most solid-state electronic structure calculations were based upon quantum electrons and classical nuclei. These calculations either omitted quantum zero-point motion and tunnelling, or estimated it in an extra step. Such quantum effects were especially significant for light nuclei, such as a proton or μ+. A simple approach was proposed for the inclusion of such quantum behaviour in a form that could be easily integrated with electronic structure calculations. This approach was demonstrated for a number of vacancy-containing defect complexes. The results suggested that, for the NHV- complex, quantum motion of the proton between 3 equivalent potential energy minima was sufficiently rapid to time-average measurements at X-band frequencies.

Quantum Behaviour of Hydrogen and Muonium in Vacancy-Containing Complexes in Diamond. A.Kerridge, A.H.Harker, A.M.Stoneham: Journal of Physics - Condensed Matter, 2004, 16[47], 8743-51