An isothermal Molecular Dynamics simulation method has been applied to the study of motions of steps on Si(100). The steps have a monolayer height and their temperature is below the roughening transition (i.e. T≤ 1000K). The calculations predict spontaneous motions even in this low temperature range and describe the functional dependence of the displacements of step-edge atoms on the step geometry, size and temperature and on the nature of the interatomic forces. Owing to the use of the Fourier analysis, these results can be applied to structures of realistic size by a proper scaling of the wavevectors.