THEORY OF KINK AND DOMAIN-WALL EXCITATIONS IN TRANSLATIONALLY-INVARIANT LATTICES WITH QUARTIC ANHARMONICITY

A theoretical investigation has been made of localized excitations hav ing the form of kinks or domain walls in translationally invariant mon atomic lattices with harmonic and quartic anharmonic interactions betw een nearest-neighbor atoms. Antisymmetric kinks are found for negative values of the anharmonic coefficient. Symmetric kinks are found to be poorly defined for translationally invariant anharmonic potentials. I n the case of domain walls, stable solutions were obtained only for ne gative values of the anharmonic coefficient. These results are compare d with those for on-site quartic anharmonicity.