By the method of density functional theory (B3LYP, 6-31G **) three types of displacements are calculated, namely oscillations as a whole, rotation and diffusion of dimers > Ge = Ge <, > Ge = Si < and > Si = Si <, which are formed on the crystalline surface of Si (001) (4×2) during the deposition of germanium atoms under conditions of molecular beam epitaxy. Calculations of angles of buckling of addimers are carried out. It is shown that when the addimers as a whole oscillate around the equilibrium position, the energy barriers are quite low, the highest of them occurs for a mixed addimer > Si = Ge <. Pure adders > Ge = Ge < and > Si = Si < oscillate between two degenerate states with an energy barrier of 0.042 and 0.014 eV, respectively. The structures of the transition state and the intermediate when the addimer > Ge = Ge < is moved between adjacent cells in the approximation of the constant bond length > Ge = Ge < are obtained. As calculations have shown, all transformations of surface dimers occur with relatively small activation energies, the numerical values of which agree satisfactorily with the results of STM experiments available in the literature.
Transformation of addimers >Ge=GeGe=SiSi=Si< on the relaxed side of Si (001) (4 × 2)
