First-principles study of length dependence of conductance in alkanedithiols

Electronic transport properties of alkanedithiols are calculated by a first-principles method based on density functional theory and nonequilibrium Green's function formalism. At small bias, the I-V characteristics are linear and the resistances conform to the Magoga's exponential law. The calculated length-dependent decay constant gamma which reflects the effect of internal molecular structure is in accordance with most experiments quantitatively. Also, the calculated effective contact resistance R-0 is in good agreement with the results of repeatedly measuring molecule-electrode junctions.