The adsorption selectivities between dithiothreitol (DTT) and 1,4-butanedithiol 2,3-diamino (BDD) were revealed through density functional theory (DFT) calculations. DFT calculations predict that DTT does not stably adsorb onto the Ge(100) surface because both hydroxyl and thiol group in DTT serve as similar nucleophilic groups, therefore they are not selective. However, BDD is predicted to adsorb stably onto the Ge(100) surface because the amine and thiol groups in BDD operate relatively different nucleophilic group, and it is selective. The adsorption energies of BDD onto the Ge(100) surface suggested that an S-H dissociated N2-H dissociation bonded structure is the most stable structure. (C) 2013 Elsevier B. V. All rights reserved.