Quantum diffusion of muonium in the alkali halides

Electronic-structure calculations are described for muonium in NaF, giving a value for the transfer-matrix element {}t⁽⁰⁾{}{}9 mK and a muonium-phonon coupling strength characterized by a deformation potential {}Ed{}{}2.6 eV. When used in the small polaronic quantum diffusion model, these values do give the crossover from coherent to incoherent tunneling at {~}100 K, as observed in other alkali halides. However, a large upward renormalization of {}t⁽⁰⁾{} is needed if this theory is to give the observed tunneling rates.