Both stationary and moving intrinsic anharmonic gap modes are generated in a perfect one-dimensional diatomic chain. For the diatomic chain the even-parity anharmonic mode is unstable against conversion to an odd-parity mode while the odd-parity mode shows long term stability, in contrast with the result found earlier for a monatomic chain. Part of the mean energy of the odd-parity gap mode is associated with kinetic and potential terms of the ac vibration while the rest resides in a localized dc distortion of the lattice. Strongly localized gap modes can be approximated by the dynamics of a triatomic molecule. For larger vibrational amplitudes and associated dc distortions, the potential for the gap mode becomes double valued and the rotating wave approximation fails. |

- Introduction
- Eigenvectors
- Even-parity gap mode instability
- Odd-parity mode frequency and lifetime
- Power spectrum
- Moving intrinsic gap mode