Beginning of epitaxial growth of vapor deposition on (0 0 1) surface has been studied by use of molecular dynamics. The activation energies of motion and conversion can be calculated using an embedded atom potential at any temperatures. The activation energy of the motion of a gold adatom on (0 0 1) surface of gold is calculated to be 0.41 eV The activation energies of dissociation in the direction of a di-adatom is 0.72 eV from the nearest neighbor to the next nearest neighbor, and 0.27 eV from the next nearest neighbor to the third neighbor. Butterfly motion of a di-adatom is 0.42 + 0.12 eV = 0.54 eV, Tri-adatoms are classified by the angle between the two bonds in the adatoms and the lengths of the two bonds. The conversion energies of tri-adatoms have also been calculated. The activation energy for the motion of an adatom on (0 0 1) surface is much higher than those corresponding the motion on (I 1 1) surfaces.