Molecular adsorption of formate and carboxyl on stoichiometric CeO_2(111) and CeO_2(110) surfaces was studied using periodic density functional theory(DFT+U) calculations.Two distinguishable adsorption modes(strong and weak) of formate are identified.The bidentate configuration is more stable than the monodentate adsorption configuration.Both formate and carboxyl bind at the more open CeO_2(110) surface are stronger.The calculated vibrational frequencies of two adsorbed species are consistent with the experimental measurements.Finally, the effects of U parameters on the adsorption of formate and carboxyl over both CeO_2 surfaces were investigated.We found that the geometrical configurations of two adsorbed species are not affected by different U parameters(U=0,5,and 7).However,the calculated adsorption energy of carboxyl pronouncedly increases with the U value while the adsorption energy of formate only slightly changes(<0.2 eV). The Bader charge analysis shows the opposite charge transfer occurs for formate and carboxyl adsorption where the adsorbed formate is negatively charge while the adsorbed carboxyl is positively charged.Interestingly,with the increasing U parameter,the amount of charge is also increased. Molecular adsorption of formate and carboxyl on stoichiometric CeO 2 (111) and CeO 2 (110) surfaces was studied using periodic density functional theory (DFT + U) calculations. Two distinguishable adsorption modes (strong and weak) of formate are identified. Bidentate configuration is more stable than the monodentate adsorption configuration. Both formate and carboxyl bind at the more open CeO 2 (110) surface are stronger. calculated vibrational frequencies of two adsorbed species are consistent with the experimental measurements. Finaally, the effects of U parameters on the adsorption of formate and carboxyl over both CeO 2 surfaces were investigated. We found that the geometrical configurations of two adsorbed species are not affected by different U parameters (U = 0,5, and 7). However, the calculated adsorption energy of carboxyl pronouncedly increases with the U value while the adsorption energy of formate only slightly changes (<0.2 eV). The Bader charge analysis shows the opposite charge tran sfer occurs for formate and carboxyl adsorption where the adsorbed formate is negatively charge while the adsorbed carboxyl is being charged. Interestingly, with the increasing U parameter, the amount of charge is also increased.