中文摘要：

在材料领域杂质原子的迁移是一个基础而永恒的主题．采用基于密度泛函理论的第一性原理方法，研究了氧原子在仪钛（a-Ti）晶体中的间隙占位情况，并计算了氧原子稳定占位点间隙能、电子态密度、电荷差分密度及其邻近钛原子的位移情况．采用基于过渡态搜索理论的CI—NEBfclimbingimagenudgedelasticband）方法预测了稳定态氧原子在α—Ti晶体中的扩散路径、扩散势垒及相应的跳转频率，并由此推算出氧原子在不同位点之间跳转的扩散系数．研究结果表明，间隙氧原子在六角密排钛晶体结构中共有七种占位，但仅存在三个可稳定占据的间隙位点：八面体中心位点、六面体中心位点及0．28nm钛一钛键中心位点．各稳定间隙位点之间的扩散具有不对称性，因此可确定三种稳定间隙氧原子位点间存在七条独立扩散路径．获取计算不同路径扩散系数所需要的微观参数，包括扩散势垒、扩散长度、不同扩散路径上鞍点氧原子的跳转频率，最终预测了不同间隙位点之间氧原子的扩散系数值，其中八面体中心扩散到邻近键位的扩散系数与实验值相符合．通过对间隙氧原子扩散行为的深入了解，希望能对控制钛合金中氧的扩散、提高钛金属中氧的含量及相关研究提供基础理论支持．

英文摘要：

How impurity atoms move through a crystal is a fundamental and renewed issue in condensed matter physics and materials science. Diffusion of oxygen （0） in titanium （Ti） affects the formation of titanium-oxides and the design of Ti- based alloys. Moreover, the kinetics of initial growth of titania-nanotubes via anodization of a titanium metal substrate also involves the diffusion of oxygen. Therefore, the understanding of the migration mechanism of oxygen atoms in c~-Ti is extremely important for controlling oxygen diffusion in Ti alloys. In this work, we show how the diffusion coefficient can be predicted directly from first-principles studies without any empirical fitting parameters. By performing the first-principles calculations based on the density functional theory （DFT） through using the Vienna ab initio Simulation Package （VASP）, we obtain three locally stable interstitial oxygen sites in the hexagonal closed-packed （hcp） lattice of titanium. These sites are octahedral center （OC） site, hexahedral center （HE） site, and Ti--Ti bond center crowdion （CR） site with interstitial energies of -2.83, -1.61, and -1.48 eV, respectively. From the interstitial energies it follows that oxygen atom prefers to occupy the octahedral site. From electronic structure analysis, it is found that the Ti--O bonds possess some covalent characteristics and are strong and stable. Using the three stable O sites from our calculations, we propose seven migration pathways for oxygen diffusion in hcp Ti and quantitatively determine the transition state and diffusion barrier with the saddle point along the minimum energy diffusion path by the climbing image nudged elastic band （CI-NEB） method. The microscopic diffusion barriers （AE） from the first-principles calculations are important for quantitatively describing the temperature dependent diffusion coefficients D from Arrhenius formula , where is the jumping frequency and L is the atomic displacement of each jump. The jumping frequency v＊ is