Nuclear quantum and H/D isotope effects of bridging and terminal hydrogen atoms of diborane (B₂H₆) molecules were systematically studied by classical ab initio molecular dynamics (CLMD) and ab initio path integral molecular dynamics (PIMD) simulations with BHandHLYP/6‐31++G** level of theory at room temperature (298.15 K). Calculated results clearly show that H/D isotope effect appears in the distribution of hydrogen (deuterium) of B₂H₆ (B₂D₆). Geometry of B₂H₆ also plays a significant role in the nuclear quantum effect proved by PIMD simulations, but slightly deviated from its equilibrium structure when simulated via CLMD simulation. The bond lengths between boron atoms R (B1 … B2) and the bridging hydrogen atoms R_HH (H_B1 … H_B2) of the B₂H₆ molecule obtained from PIMD simulations are slightly longer than those of the deuterated form of the diborane (B₂D₆) molecule. The principal component analysis (PCA) was also employed to distinguish the important modes of bridging hydrogen as related to the nuclear quantum and H/D isotope effects. The highest level of contribution obtained from PCA of PIMD simulations is bending, while various mixed vibrations with less contribution were also found. Therefore, the nuclear quantum and H/D isotope effects need to be taken into account for a better understanding of diborane geometry.

中文翻译：

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核量子和氢同位素对三中心键合乙硼烷的影响：路径积分分子动力学模拟

通过经典的从头算分子动力学（CLMD）和从头算路径积分分子动力学（PIMD）模拟，以BHandHLYP / 6系统研究了乙硼烷（B ₂ H ₆）分子桥接和末端氢原子的核量子和H / D同位素效应‐31 ++ G **室温（298.15 K）时的理论水平。计算结果清楚地表明，H / D同位素效应出现在B ₂ H ₆（B ₂ D ₆）的氢（氘）分布中。B ₂ H _6的几何在通过PIMD模拟证明的核量子效应中也发挥了重要作用，但通过CLMD模拟进行模拟时，其平衡结构略有偏离。通过PIMD模拟获得的B ₂ H ₆分子中的硼原子R（B1…B2）和桥连氢原子R _HH（H _B 1…H _B 2）之间的键长略长于氘代形式的乙硼烷（B ₂ D ₆）分子。还使用主成分分析（PCA）来区分桥接氢的重要模式，这些模式与核量子和H / D同位素效应有关。从PIMD模拟的PCA获得的最大贡献水平是弯曲，同时还发现了各种混合振动，但贡献较小。因此，为了更好地了解乙硼烷的几何形状，需要考虑核量子和H / D同位素效应。