| Although vibrational localized modes associated with impurities in crystals have been studied for many years, it was not until the late 1980's that theoretical evidence was found for localized modes in perfect 1-D anharmonic crystals. Interest in these intrinsic localized modes continues to grow since they appear to form an integral part of the vibrational description of a strongly anharmonic system in terms of effective harmonic oscillators. It is the purpose of this tutorial to provide both qualitative and quantitative illustrations of these localized vibrational modes for 1-D lattices with different kinds of anharmonic potentials. |