Search

The O2 dissociation and O atoms adsorption on free-standing germanene are studied by using first-principles calculations in this letter. Compared with the spontaneous dissociation of oxygen molecule on free-standing silicene in air, germanene is more stable than silicene from kinetic point of view, with overcoming energy barrier of about 0.55 eV. Especially, in contrast with the unique chemical adsorption of O2-dissociation-induced O atoms on silicene, oxygen molecule can behave a correspondingly stable adsorption on germanene surface. Moreover, single O atom adsorption on germanene is also different to that on silicene, resulting in two opposite migration pathways on germanene surface. Furthermore, once the oxygen molecule dissociates into O atoms on germanene surface, the migration and desorption of O atoms are relatively difficult under room temperature due to the strong Ge-O bonds in the O-adsorbed germanene, in favor of forming germanium oxides. The results provide compelling evidence to show that free-standing gemanene is relatively stable in oxygen,which is different to silicene essentially.

The oxygen adsorption and dissociation on pristine silicene surface are studied by use of first-principles in this letter. The oxygen adsorption and dissociation on pristine silicene surface are studied by use of first-principles in this letter. It is found that the pristine silicene is not stable in air because the oxygen molecule can be easily adsorbed and dissociated into two O atoms without overcoming any energy barrier on pristine silicene surface. In addition, dissociated oxygen atoms are relatively difficult to migrate on or desorbed from pristine silicene surface, leading to poor mobility of oxygen atom. As a result, silicene would be changed into Si-O compounds in air. The work will be helpful to reveal the detail of the interaction between oxygen molecules and pristine silicene surface, especially helpful to understand the stability of silicene in air.

Structural and electronic properties of the lambda-MnO2(001) surface are investigated applying density functional theory approach. The calculations show that all Mn ions at unreconstructed smooth surface preserve the +4 oxidation state observed in the bulk. Upon the lambda-MnO2(001) reconstruction, one fourth of Mn ions at the surface undergo a change of the oxidation state from +4 to +3, although the reconstruction does not change the Mn coordination number with oxygen. This is accompanied with the filling of initially empty 3d(z2) states localized on cations with one electron denoted by two neighboring O atoms. Although the reconstruction leads to an energy gain of 0.04 eV per surface unit cell, it is not a spontaneous process since it proceeds with an activation energy of 0.12 eV. (C) 2010 American Institute of Physics. [doi:10.1063/1.3509401]

LiMn2O4 is one of the important cathode material for rechargeable lithium batteries. Standard ab initio studies within local density approximation (LDA) and generalized gradient approximation (GGA) are not able to reproduce the intrinsic insulating electronic structure and Jahn-Teller-type local atomic distortion of LiMn2O4. In the present work, GGA+U method is shown to be able to localize electrons to Mn 3d(z2) orbits in the majority spin channel, and open a gap of about 0.5 eV between the Mn 3d(z2) and Mn 3d(x2-y2). Results from GGA+U calculation showed that Mn ions are in the mixed valence state of Mn3+ and Mn4+. This is in good agreements with experimental observations and different to Mn3.5+ obtained from standard GGA calculations. While Jahn-Teller distortion is not observed in Mn4+O6 octahedra, it is clearly seen in Mn3+O6 octahedra, in which Mn-O bond lengths along the z-axis direction are obviously elongated. (C) 2008 Elsevier B.V. All rights reserved.

Li1+xFePO4 (0