BiOCl{001}表面原子与电子结构的第一性原理研究

Study on the atomic and electronic structures of BiOCl{001} surface using first principles

基于密度泛函理论的第一性原理方法研究了BiOCl{001}的三种不同终端面({001}-1Cl,{001}-BiO和{001}-2Cl)的表面弛豫、能带结构、电子态密度和表面能.计算结果表明:{001}-1Cl,{001}-BiO和{001}-2Cl表面均发生明显弛豫,而在双Cl原子层处的层间距变化较大,但未出现振荡弛豫现象,其中{001}-1Cl表面弛豫较小.与体相BiOCl电子结构相比,BiOCl{001}面具有较窄的带隙宽度,并呈现较强局域性:对于{001}-BiO表面,其导带与价带均往低能方向发生较大移动,并且在导带底部出现表面态;而{001}-2Cl表面的表面态主要出现在价带顶;{001}-1Cl表面的带隙中则无表面态产生;表面态的出现导致{001}-BiO面和{001}-2Cl面带隙明显减小.BiOCl{001}三种终端表面的表面能分析结果表明,{001}-1Cl表面的表面能最小(0.09206J.m^(-2)),结构最稳定,而{001}-BiO表面和{001}-2Cl表面的表面能分别为2.392和2.461J.m^(-2).理论预测{001}-BiO表面和{001}-2Cl表面具有较高的活性,但在BiOCl晶体生长过程中不易暴露.本文计算结果为实验获得BiOCl高活性面{001}给予了基础理论解释,进一步为BiOCl新型光催化材料的应用研究提供理论指导.

The surface relaxations,band structures,densities of states and surface energies of BiOCI{001}surfaces containing{001}-1C1,{001}-BiO and{001}-2C1 are studied using first-principles based on density functional theory.The calculated results indicate that there exist obvious relaxations for the three types of{001}surfaces,especially for their double chlorine layers.The relaxation result of{001}-IC1 surface is the minimum one in the BiOCI{001}surfaces.Compared with the electronic structure of bulk BiOC1,BiOCI{001}surfaces exhibit the smaller band gap and stronger localized energy levels.Besides,both conduction and valence band of{001}-BiO shift towards the lower energy and there exist surface states at the bottom of conduction band.For{001}-2C1,surface states are located at the top of valence band.The occurrences of these surface states can lead to the obvious reductions of band gaps for{001}-BiO and{001}-2C1.Furthermore,the surface energy of BiOCI{001}is calculated and investigated.The analysis results show that surface energies of{001}-1C1,{001}-BiO and{001}-2C1 are 0.09206 J.m-2,2.392 J.m^(-2)and 2.461 J-m^(-2),respectively.Thus the{001}-1C1 possesses the minimum surface energy and the highest stability,while{001}-BiO and{001}-2C1 exhibit the higher reaction activities and are difficult to be exposed in the growth process of BiOC1 crystal.Our obtained results provide the theoretical guidance for the further understanding of the facet-dependent photoreactivity of BiOC1,the fine manipulation of their photoreactivity,and the progress of actual application for BiOC1 photocatalytic material.