Using the Hartree-Fock Roothaan scheme we have carried out molecular cluster calculations to study the interaction of positive muon with host metal atoms and intrinsic lattice defects in lithium. The total ground state energies of the clusters are calculated selfconsistently for various assumed impurity-host configurations. From the minimum in the total energy curve, we are able to determine the equilibrium lattice constant, the relaxation of first near neighbors around the impurity, the binding energy of the muon to a lattice trap and the activation energy for muon diffusion. Extension of the present method to treatμ +-defect complexes in other metallic hosts are discussed.