By means of computer simulation of a copper lattice, we have found two resonance modes of the (split) interstitial configuration. The low frequencies of about $\frac{{\omega }_{max}}{7}$ are due to the strong negative "leaf springs" typical for the strongly compressed lattice around the interstitial atom. It seems very likely that many longstanding problems associated with point defects can be explained in terms of such modes.

• Received 17 September 1973

DOI:https://doi.org/10.1103/PhysRevLett.31.1130