The energies of the ideal (1 x 1), dimer (2 x 1) and trimer (3 x 1) structures on (0 0 1) surfaces have been calculated by using MEAM for three diamond cubic crystals C, Si and Ge. From energy minimization, the dimer (2 x 1) and trimer (3 x 1) reconstructions can be formed naturally and without any barrier. The dimer corresponding to the lowest energy implies it is the easiest to be formed and the most stable as well. This is consistent with the experimental result and other theoretical prediction. Determined dimer bond length of 2.43 angstrom for Si drops in the experimental range of 2.20-2.47 angstrom, and of 2.5 angstrom for Ge is close to the 2.55 angstrom measured by X-ray diffraction. The trimer, constructed here firstly, has not been observed in the experimental due to its slightly higher energy than dimer. Its bond lengths have been determined to be 1.96, 2.64 and 2.75 angstrom for C, Si and Ge, respectively. Further experimental testing is needed. (C) 2008 Elsevier B.V. All rights reserved.