Theoretical analyses of phase transition and Debye-Waller factor of Si(111)-Ag root 3x root 3 surface

According to the recent STM measurements and first principles calculations, the ground state structure of Ag adsorbed Si(1 1 1) surface is the inequiv alent triangle (IET) structure not but the honeycomb chained triangle (HCT) structure. A simplified theoretical model to describe the phase transition from HCT to IET is introduced. The interaction parameters in the model Ham iltonian are estimated from the first principles calculation based on the d ensity functional theory, The properties related to the phase transition an d the Debye-Waller (D-NV) factor are calculated with the Monte Carlo simula tion, The calculated D-W factor takes the relatively large value correspond ing to the thermal fluctuation of the surface Ag atoms and it qualitatively agrees with the experimental one. (C) 2001 Elsevier Science B.V, All right s reserved.