Atomic scale simulations are performed for the ion bombardment induced roughening of the amorphous diamond films, when the films are deposited by using kiloelectronvolt mass separated ion beams operated in the upper limit of practical deposition energies up to 20 keV. The results show that the roughness due to sputtering erosion is by a factor of 3 to 4 larger than roughness observed in experiments. The experimentally observed roughness is obtained only when moderate surface relaxation within the distance of next nearest neighbors is included in the simulations. The results suggest that atomic scale relaxation of sputtering induced topography occurs during the deposition. ©1997 American Institute of Physics.