Effect of local defects on vibrational characteristics of infinite and semi-infinite one-dimensional structures in an external periodic field

Exact analytic expressions for Green's functions of the chain type structur es with defects in an external periodic field are obtained by the method of Jacobi matrices. A diatomic impurity molecule in a monatomic chain as well as adsorbed chains with a monatomic and a diatomic unit cell are considere d. The conditions for the formation and the characteristics of local and ga p vibrations are investigated. The evolution of the threshold values of mas s of the defect required for the formation of localized vibrations by two i sotopic impurities upon a change in the separation between them is analyzed . (C) 1999 American Institute of Physics. [S1063-777X(99)01101-9].