QUANTUM-MECHANICAL STUDY OF FRICTION IN NANOCONTACTS

Abstract

The quantum-mechanical approach (the density functional theory and the pseudopotential method) is used to study the friction in the aluminum–aluminum, aluminum–tungsten, and tungsten–tungsten nanopairs on the atomic level in the presence of external pressure. Nanopairs were constructed from crystalline nanoslabs and crystalline nanorods of rectangular cross section. The nanoslabs had infinite periodic structures in the X and Y directions; the nanorods were periodic in the Y direction. The process of friction was studied by reducing a rod and a slab to an equilibrium contact with subsequent step-by-step shift of the rod relative to the slab along the X direction. The rod was located above the slab (in the Z direction). The total energy of the system was calculated on each step. The friction force was calculated as a ratio of the change in the total energy to the value of the rod shift step. The pressure force was applied to the rod in the Z direction. The coefficient of friction was calculated as a ratio of the friction force to the pressure force. Observation of the behavior of atoms showed that for all the nanopairs studied the process of friction is accompanied by the processes of deformation and destruction. Both components of a nanopair are subjected to deformation, whereas destruction is observed only in the nanorods. Aluminum rods are subject to the maximum deformations and destructions in both aluminum–aluminum and aluminum–tungsten pairs. The tungsten rods are not destroyed; deformations in them and in tungsten slabs are minimal. The friction coefficients in the aluminum–aluminum pairs decrease with increasing pressure, and they increase in the aluminum–tungsten and tungsten–tungsten pairs.