[1] Xue Y, Datta S, Hong S, Reifenberger R et al 1999
Phys. Rev. B 59 7852

[2]Lang N D and Avouris Ph 1998 Phys. Rev. Lett. 81 3515

[3]Havu P, Torsti T, Puska M J and Niemine R M 2002
Phys. Rev. B 66 75401

[4]Larade B, Taylor J, Mehrez H and Guo H 2001 Phys. Rev. B
64 075420

[5]Emberly E and Kirczenow G 1999 Nanotechnology 10 285

[6]Grigoriev C A, Wendin G and Stokbro K 2005 Phys. Rev. B
71 165316

[7] Roland C, Meunier V, Larade B and Guo H 2002 Phys. Rev.
B 66 035322

[8] Guti R\'errez, Grossmann F, Knospe O and Schmidt R 2001
Phys. Rev. A 64 013202

[9]Majumder C and Kulshreshtha S K 2004 Phys. Rev. B
69 075409

[10]Brandbyge M, Mozos J L, Ordejon P, Taylor J and Stokbro K
2002 Phys. Rev. B 65 165401

[11]Taylor J, Guo H and Wang J 2001 Phys. Rev. B 63 245407

[12]Jose M S et al 2002 J. Phys. Condens. Matter.
14 2745

[13] Heurich J, Cuevas J C, Wenzel W and Sch\"{on G 2002
Phys. Rev. Lett. 88 256803

[14] Zhou Y H, Zheng X H, Xu Y and Zeng Z Y 2006 J. Chem.
Phys. 125 244701