Quantum diffusion of atomic species in metals

The coefficient of quantum diffusion D(T) is calculated using exact states of the localized impurity in the deformed vibrating lattice. Without resorting to the Born-Oppenheimer approximation an explicit general expression for D(T), valid for impurities of arbitrary mass and holding in the whole range of temperature, is obtained in terms of the crystal properties. Interesting new features arise from retaining some terms of the Hamiltonian which were left aside in previous theories.