VO2 is an attractive material for application to thermochromic optoelectronic devices such as smart windows, and Ag/VO2 double-layered structure can effectively decrease the phase transition temperature (T-c) of VO2 thin film, which is very important for practical application of VO2. Previous works has shown that the decrease in phase transition temperature (T-c) seems to be relevant with the work function of VO2 in Ag/VO2 double-layered thin film, although the underlying mechanism of tuning its Tc by Ag incorporation and adsorption on the VO2(1 0 0) surface has been rarely investigated. Our first-principles calculations reveal that the adsorption of Ag atoms on the VO2(1 0 0) surface rather than incorporation of Ag exhibits a lower work function, which is ascribed to an integrated effect of charge transfer from Ag to VO2(1 0 0) surface and enhanced surface dipole moment. The results suggest that the decrease in work function of VO2 with Ag adsorption favors the reduction in T-c. The current findings are helpful to understand the fundamental mechanism for yielding high-efficiency VO2-based optoelectronic devices. (C) 2016 Elsevier B.V. All rights reserved.