  A deterministic theory describing the melting of an ultrathin lubricant film
between two atomically smooth solid surfaces has been developed. The lubricant
state is described by introducing a parameter of excess volume that arises
owing to the solid structure chaotization at its melting. The thermodynamic and
shear kinds of melting are described consistently. The dependences of the
stationary friction force on the lubricant temperature and the shear velocity
of rubbing surfaces that move with respect to each other with a constant
velocity have been analyzed. In the framework of a simple tribological model,
the stick-slip mode of friction, when the lubricant periodically melts and
solidifies, has been described. The influence of velocity, temperature, and
load on the stick-slip friction has been analyzed. A qualitative comparison
between the results obtained and experimental data has been carried out.
