The adsorption modes and electronic structure of formaldehyde on TiO2(110) were investigated using the PWDFT method. The eta(1)(O) adsorbed mode has two stable structures: perpendicular to surface plane and tilted along the [110] direction. The eta(1)(O) tilt geometry is similar to 25 kJ/mol more stable than the eta(1)(O) straight geometry. In the case of tilted adsorption, orbital 2b(2) of formaldehyde (HOMO; O2p(x)) has considerable overlap with Ti3d states while in the case of perpendicular adsorption, orbital 5a(1) (HOMO-2; O2p(z)) has the strongest overlap. All lower energy adsorbed formaldehyde orbitals have better Ti overlap in the straight configuration, however. (C) 2013 Elsevier B.V. All rights reserved.