氢化铁的自旋极化效应及势能函数

B3LYP/6-311++g**水平上预测了FeH2及FeH稳定构型讨论了其自旋极化效应,并与实验结果进行了比较.结果表明其基态分别为FeH2(5A1)和FeH(4?),自旋态对构型和物理性质均有显著影响.FeH2具有C2v对称性.势能与核间距的关系用4参数Murrell-Sorbie函数进行拟合得到其分析势能函数.由此推导出力常数和光谱数据,并由多体项展式理论导出了基态FeH2分子的分析势能函数.用这个分析势能函数分析表明:H+FeH生成FeH2(C2v)分子通道存在一个4.68 eV深的势阱,易生成H—Fe—H络合物分子.反应Fe+H2→HFeH,?H=-0.08305 eV,是放热反应.

Spin polarization and potential energy function of FeH2

Among the three methods (B3LYP, BP86 and B3LYP^*) in density functional theory (DFT), the best tools for predicting the ground state of metal hydride, the B3LYP method for predicting the harmonic frequencies and geometric parameters of the ground state of FeH₂ gives result in good accordance with the experimental data; so it is employed to optimize the structure of molecules FeH and FeH₂ in possible geometries and multiplicities based on 6-311++g(d,p) level in searching of the structure with the lowest energy. Results show that their electronic states in the ground states are FeH(⁴Δ) and FeH₂(⁵A₁), supposing that the two molecules have three and four unpaired electrons respectively, with spin polarization effect, and they are paramagnetic substances, and the stable structure of molecule FeH₂ is of C_2v symmetry. The Murrell-Sorbie potential energy function-the sufficient analytical potential function form for biatomic molecules-with 4 parameters in molecule FeH is derived via the least square method. Their spectra data and force constants are deduced according to the results. The analytical potential energy function of FeH₂ is also obtained from the many-body expansion theory, which gives the analytical potential function of triatom molecules of the single-value potential surface consisting of three parts with single body terms, two body terms, and three body terms. The deduced analytical functions for FeH₂ in this paper predict successfully a global minimum stable structure of quintet FeH₂ with a 4.68 eV depth potential trap, and other higher energy stable and saddle structures. This potential function predicts the balanced ground structure and the second derivative force constants of this molecule. According to the potential function of FeH₂(C_2v), when it is formed from H and FeH, a potential trap with its depth being 4.68 eV is excited and the complex molecule of H–Fe–H is easily formed. The reaction of Fe+H₂ → HFeH is exothermic with ΔH=-0.08305 eV.
Keywords： hydride iron density functional theory (DFT) spin polarization potential energy function