STABILIZATION OF THE ASYMMETRIC GE DIMER ON SI(100) BY CHARGE-TRANSFER

The DMol first-principles molecular-cluster total-energy and atomic-fo rce approach is used to study the Ge dimer on the Si(100) surface with clusters containing up to 85 atoms. It is shown that the Ge asymmetri c dimer is energetically more stable than the symmetric dimer due to c harge transfer from a down dimer atom to an up atom even though this a ccompanies a weakening of the covalent bonding between the dimer atoms . By calculating the forces on atoms in the first three Si layers and minimizing the total energy of the cluster, the optimized atomic geome try is obtained. The calculated dimer height displacement of this buck led dimer is shown to be 0.60 Angstrom and the tilt angle is 14.2 degr ees. The magnitude of this buckling lies between the range that was ca lculated for clean Si(100)2X1 and Ge(100)2X1 using the same approach, which agrees with the experimental measurements for those surfaces.