A first-principles theoretical study was made of muonium and H impurities. A spin-polarized density-functional method was used, with the crystalline orbitals expanded into all-electron Gaussian basis sets. The behavior of H and muonium at both the tetrahedral and bond-centered sites was investigated within a super-cell approximation. In order to describe the zero-point motion of the impurities, a double adiabatic approximation was used in which the electron, muon/proton, and host-lattice degrees of freedom were decoupled. Within this approximation, the relaxation of the host-lattice atoms could differ for the muon and proton although, in practice, the difference was slight. Upon including the zero-point motion, the tetrahedral site was energetically preferred over the bond-centered site. The hyperfine and superhyperfine parameters, when calculated as averages over the motion of the muon, agreed quite well with available data on muon spin resonance.

Muonium as a Hydrogen Analogue in Silicon and Germanium - Quantum Effects and Hyperfine Parameters A.R.Porter, M.D.Towler, R.J.Needs: Physical Review B, 1999, 60[19], 13534-46