第一性原理研究BaTiO_3(001)表面的电子结构

First-principle study on electronic structure of BaTiO_3(001) surfaces

在密度泛函理论的基础上,采用平面波赝势方法计算了立方相BaTiO3(001)表面的电子结构.结构优化表明最表层原子都向体内弛豫,且金属原子弛豫幅度最大,同时各层层间距变化呈交错分布.对两种表面结构的总能计算发现TiO2表面稳定性比BaO表面弱,一方面是由于TiO2表面结构中存在O-2p表面态,使价带和导带中电子态向高能区域偏移.另一方面,TO2表面附近Ti—O共价键存在强弱差异,有利于发生表面吸附.而在BaO表面结构中,最表层BaO的存在消除了这种差异,因而其表面稳定性较强.

Electronic structures of the （001） surface of cubic phase barium titanate have been calculated by using plane-wave pseudopotential method within the density functional theory. Geometry optimization indicates that the largest atomic relaxation occurs to metal atoms in surface layers where all atoms are ＂displaced inward, and the interlayer distances vary alternately. Total energy calculation shows that the TiO2-terminated surface is unstable compared with that with BaO termination. One reason is that surface state of O-2p orbital observed in band structure of TiO2 termination helps the electron state shift towards higher energy region in both valence band and conduction band. Redistribution of electrons near surface region in TiO2 termination also provides evidence that intensity of covalent bonding between Ti and O atoms differs and hence TiO2 termination is more suitable for surface adsorption. In contrast, such difference was eliminated in BaO termination, accounting for its superiority in surface stability.