Аннотация:Studied in the present work is is the focusing of parallel ion beam by a pair of close packed atomic chains of a crystal. The focal length of this system has been calculated to the approximation of continuous potential of chain in the general form and also for a number of specific potentials of ion-atom interaction. Ar ion beam focusing by a <110> Cu chain pair has been discussed in details. For this case, the focal length has been calculated as a function of ion energy using the method of computer simulation of ion trajectories in the chain field. The calculations were made on the basis of the Born-Mayer potential with various constants. A pronounced dependence of focal length on the constants in this potential has been found.