中文摘要：

用密度泛函理论的B3lyp方法,Ti原子采用相对论有效实势（LanL2DZ）收缩价基函数,氢原子采用6-311＋＋G^＊＊全电子基函数,对TiH2体系的结构进行优化计算.得到TiH2分子最稳态为C2v构型,电子状态为（C2vX^~3A2）,平衡核间距,RTi-H=0.1789 nm,键角∠HTiH=123.365°,离解能：De=5.54216 eV.基态简正振动频υ（A1）=485.4150 cm^-1,υ（B2）=1507.6533 cm^-1,υ（A1）=1580.2361 cm^-1.由微观过程的可逆性原理分析了分子的可能离解极限,并用多体项展式理论方法分别导出基态TiH2分子的势能函数,其等值势能面图准确地再现了TiH2分子的结构特征和离解能.由此讨论了TiH2分子反应的势能面静态特征.

英文摘要：

Based on the relativistic effective core potential （RECP） for Ti atom and 6-311 ＋ ＋ G^＊＊ basis sets for H atom, the equilibrium structure of TiH2 has been optimized by using density functional theory （DFT）/ B3lyp method. It has a bent （C2vX^~3A2） ground electronic state with an angle of 123.365°. The vibronic fiequencies and force constants have also been calculated. The possible electronic states and reasonable dissociation limits for the ground electronic state of TiH2 molecule have been determined by using the principles of atomic and molecular reaction statics. And the analytic potential energy function of TiH2 （X^~3A2） molecule has been derived by using the many-body expansion theory. The contour lines are also constructed, which show the static properties of TiH2（X^~3A2）, such as the equilibrium structure, the lowest energies, etc. The potential energy surface of TiH2 （X^~3A2） is reasonable and very satisfactory.