Muonium as a hydrogen analogue in silicon and germanium: Quantum effects and hyperfine parameters

We report a first-principles theoretical study of hyperfine interactions, zero-point effects, and defect energetics of muonium and hydrogen impurities in silicon and germanium. The spin-polarized density-functional method is used, with the crystalline orbitals expanded in all-electron Gaussian basis sets. The behavior of hydrogen and muonium impurities at both the tetrahedral and bond-centered sites is investigated within a supercell approximation. To describe the zero-point motion of the impurities, a double adiabatic approximation is employed in which the electron, muon/proton, and host lattice degrees of freedom are decoupled. Within this approximation the relaxation of the atoms of the host lattice may differ for die muon and proton, although in practice the difference is found to be slight. With the inclusion of zero-point motion the tetrahedral site is energetically preferred over the bond-centered site in both silicon and germanium, The hyperfine and superhyperfine parameters, calculated as averages over the motion of the muon, agree reasonably well with the available data from muon spin resonance experiments. [S0163-1829(99)01643-4].