Mg-Ti-H 体系晶体结构与相稳定性的第一性原理计算

采用基于密度泛函理论的第一性原理赝势平面波方法计算了不同Ti含量的MgxTi(1-x)H2(x=0.25,0.5,0.75,0.875)体系的平衡晶格结构、总能量及稳定性.结果表明:氢原子在晶胞中的位置接近于四面体间隙位置;H―Ti原子间距小于H―Mg原子间距,表明Ti较Mg具有更强的"亲氢性",Ti原子在吸引周围H原子的同时削弱了H―Mg键的强度;随Ti含量的增加,体系的稳定性和脱氢温度均降低,且MgxTi(1-x)H2体系与MgH2相比,稳定性更差,脱氢温度更低,表明Ti可降低MgxTi(1-x)H2体系的分解温度并加速其脱氢动力学过程,表现出脱氢催化活性.

First-Principles Calculation of the Crystal Structure and Stabilization of Mg-Ti-H System

First-principles calculations were performed to determine the equilibrium crystal structures,energetic properties,and stability of MgxTi(1-x)H2(x=0.25,0.5,0.75,0.875) systems containing different amounts of titanium using the pseudopotential plane-wave method based on density functional theory.The calculation results show that the hydrogen atoms in the MgxTi(1-x)H2 hydrides roughly occupy the tetrahedral interstitial sites.The calculated H―Ti distances are less than the H―Mg distances.This indicates that Ti has a more notable affinity for hydrogen than Mg.The bonding strength of H―Mg is weaker when the Ti atom attracts surrounding hydrogen atoms.The stabilization and dehydrogenation temperatures of the hydrides MgxTi(1-x)H2 are lower than those of MgH2 with an increasing Ti content.This indicates that titanium can reduce the decomposition temperature of the MgxTi(1-x)H2 hydrides and play a significant catalytic role in improving the dehydrogenation dynamic properties of the MgxTi(1-x)H2 hydrides.