  We study numerically the evolution of the velocity distribution of atoms
under the action of the bichromatic force. The comparison of the time
dependencies of the distribution width and the average acceleration of atoms
reveal the correlation of these quantities. We show that the estimation of the
momentum diffusion coefficient on the basis of the analogy between the
interaction of atoms with the counter-propagating bichromatic waves and the
interaction of atoms with the counter-propagating sequences of the $\pi$-pulses
roughly corresponds to the results of numerical calculations. To separate the
influence of the momentum diffusion on the evolution of atomic momentum
distribution from the influence of the time-dependent Doppler shift, we study
the motion of a ``heavy'' atom, for which the velocity change during the
interaction of an atom with the field can be neglected. Provided that the
parameters of the atom-field interaction are optimal, we show that the momentum
diffusion coefficient is proportional to the intensity of the laser radiation.
We used the Monte Carlo wave-function method for the numerical simulation of
the atomic motion.
