Abstract: Nano grains are single phase or multiphase polycrystals with a grain size in the range of 1 to 100 nm. Compared with bulk materials with the same chemical composition, nano grains exhibit rather high surface energy due to the large volume fraction of particles (atoms and molecules) residing in the grain boundaries. Therefore, the influence of surface energy to the mechanical properties of grain, such as Young's modules, lattice size and eigenfrequency, is not negligible. This is confirmed by experiments....