The formation and migration of polarons have important influences on physical and chemical properties of transition metal oxides.Density functional theory plus the Hubbard U correction(DFT+U)and constrained density functional theory(cDFT)are often used to obtain the transfer properties for small polarons.In this work we have implemented the cDFT plus the Hubbard U correction method in the projector augmented wave(PAW)framework,andapplied it to study polaron transfer in the bulk phases of TiO_(2).We have confirmed that the parameter U can have significant impact on theoretical prediction of polaronic properties.It was found that using the Hubbard U calculated by the cDFT method with the same orbital projection as used in DFT+U,one can obtain theoretical prediction of polaronic properties of rutile and anatase phases of TiO_(2) in good agreement with experiment.This work indicates that the cDFT+U method with consistently evaluated U is a promising first-principles approach to polaronic properties of transition metal oxides without empirical input.
6H-SiC is an important semiconductor material. The 6H-SiC wafer is always exposed to a high-humidity environment and the effect from the absorbed water molecule and some relative adsorbates is not negligible. Here, the oxygen and water molecules absorbed on the 6H-SiC(0001) surface and the dissociation process were studied with density functional theory. On the 6H-SiC(0001) surface, absorbed O2 is spontaneously dissociated into O*, which is absorbed on a hollow site, and further transforms the 6H-SiC(0001) surface into SiO2. The absorbed H2O is spontaneously broken into OH*and H*, which are both absorbed on the top of the Si atom, and OH* is further reversibly transformed into O* and H*. The H* could saturate the dangling Si bond and change the absorption type of O*, which could stabilize the 6H-SiC(0001) surface and prevent it from transforming into SiO2.
