The adsorption of benzotriazole (BTAH) on Cu2O(111) was investigated with use of first-principles density functional theory calculations. Two possible adsorption structures were considered for both one-quarter and full adsorption coverage. We found that BTAH strongly chemisorbs (1.2-1.5 eV) onto Cu2O(111) by forming a chemical bond with a surface copper atom through nitrogen sp(2) lone pairs, and a hydrogen bond with a surface oxygen atom through a C-H or N-H proton. The chemical interaction between the surface copper site and the molecule is the combined effect of a strong lone-pair --> hybrid Cu-d(z)(2)sp(z) sigma-donation and a relatively weak d(yz) --> 6pi* back-donation. Vibration calculations were carried out to predict the BTAH-Cu2O stretching frequencies for both adsorption structures. The calculated stretching frequency (381 and 428 cm(-1)) could overlap with the BTAH benzene-ring torsion band. An estimate for the BTAH-Cu vibrational frequency (226 and 223.4 cm(-1) for two adsorption modes, respectively) is in good agreement with an experimentally observed Raman peak of 240 cm(-1).