Wei-Bing Zhang

Structural distortion and electronic properties of NiO under high pressure: an ab initio GGA+U study

The structural distortion and electronic properties of NiO under high pressure are investigated by means of first-principles calculations within the density functional theory (DFT) in the generalized gradient approximation (GGA). The strong electronic correlations are also taken into account in the form of GGA + U. Recent experiments implied that previous local density approximation (LDA) calculations incorrectly predicted structural distortion under high pressure, especially above 60 GPa. The present results show that even GGA calculations do not give a proper description of structural distortion under high pressure, although much improved structural and bulk properties are obtained. When strong correlations are included, overall agreement of the structural distortions of NiO under high pressure is obtained. The lattice constants a and c as well as the axial ratio c/a are in good agreement with experiment over the entire experimental pressure range. The successful prediction of the structural distortion of GGA + U can be attributed to the reasonable description of nearest-neighbour magnetic exchange interactions. In addition, we also analyse the density of states under different pressures. Present results indicate that, with increasing pressure, the bandwidth increases and the bandgap transits from being a mixture of charge-transfer and Mott-Hubbard type towards solely Mott-Hubbard type.

Adsorption of oxygen atoms on the Mg3Nd(001) surface

Based on the density functional theory, the stability of three possible Mg3Nd(001) surfaces is investigated, and the structural and electronic properties of O adsorption on the most stable Mg3Nd(001) surface are studied. The calculated results show that the most favorable adsorption site is the (2Nd+Mg) hollow site, and the adsorption energy decreases as the coverage increases. At low coverage O atoms prefer Nd atoms to Mg atoms as nearest neighbors. When the coverage increases to a full monolayer, some O atoms sink into the alloy surface and stay between Nd and Mg atoms. The electronic structures of the adsorption system show that for all coverage the interaction between O and the alloy surface mainly arises from the hybridization of O 2p states and Nd 5d states, while the interaction between Mg 3s states and O 2p states becomes noticeable at the high coverage. The present study reveals that during the initial oxidation stage of the alloy, Nd atoms can get a priority of oxidation, followed by Nd rich oxi...