A molecular cluster approach to the electronic structure of anomalous muonium in diamond

First-principle discrete variational (DV) X? cluster calculations are used to reproduce muon spin rotation (?SR) experimental data relative to anomalous muonium in diamond. A detailed analysis of the muonium-host interaction is reported. Calculations of the Fermi contact (A), of the dipolar (2B) hyperfine (hf) parameters and of the two components of the hf interaction tensor A (A? and A?) agree well with experimental data only if an optimized numerical atomic basis set is used. Moreover, superhyperfi coupling constants for muonium at the nearest carbon atoms have been also computed. Theoretical data relative to hf quantities indicate that they do not seem to be strongly cluster-size dependent. Finally, the herein reported results have been also compared with other theoretical investigations carried out by using different approaches. The good agreement between our results and the experimental ones, coupled with the quite low computational cost of the DV-X? approach, are encouraging for further investigations of more complex systems.