Guillaume Maxime, Champagne Benoît, Bégué Didier, Pouchan Claude
Centre for Theoretical and Computational Chemistry, University of Tromsø, 9037 Tromsø, Norway.
J Chem Phys. 2009 Apr 7;130(13):134715. doi: 10.1063/1.3104629.
Electrostatic interaction schemes have been applied to predict the evolution of the polarizability in Si(n) clusters of increasing size (n=3-19). Both on-site polarization and charge transfer effects have been included in the interaction scheme, of which the values have been compared to B3LYP/6-311G() and other first principles results. To reproduce the pattern of the variation of the B3LYP average polarizability per Si atom as a function of the cluster size, the atomic polarizability employed in the interaction scheme should amount to roughly 80% of the bulk atomic polarizability. However, this results in a systematic underestimation of the polarizability per Si atom by about 25%, whereas increasing the atomic polarizability value leads to excessive variations of the polarizability per Si with the cluster size. An improved agreement is obtained when incorporating a charge transfer contribution, at least for sufficiently large clusters, substantiating the fact that in large clusters electrostatic effects are dominant over quantum effects. This charge transfer atomic polarizability term has been modeled by a simple function, which evolves linearly with the difference of Cartesian coordinates between the atom and the center of mass and that has been verified using B3LYP/6-311G() calculations. In the case of the prediction of the polarizability anisotropy, a similar atomic polarizability corresponding to 80% of the bulk atomic polarizability has been shown suitable to reproduce the B3LYP results, whereas inclusion of charge transfer effects can slightly improve the agreement, provided the amount of charge transfer increases with the size of the cluster.
静电相互作用方案已被用于预测尺寸不断增大的硅（n）团簇（n = 3 - 19）中极化率的演变。该相互作用方案中包含了局域极化和电荷转移效应，并将其值与B3LYP/6 - 311G（）及其他第一性原理结果进行了比较。为了重现B3LYP计算得到的每个硅原子的平均极化率随团簇尺寸变化的模式，相互作用方案中采用的原子极化率应约为体相原子极化率的80%。然而，这导致每个硅原子的极化率被系统地低估了约25%，而增大原子极化率值会导致每个硅原子的极化率随团簇尺寸出现过度变化。当纳入电荷转移贡献时，至少对于足够大的团簇能获得更好的一致性，这证实了在大团簇中静电效应比量子效应更占主导这一事实。这个电荷转移原子极化率项已通过一个简单函数进行建模，该函数随原子与质心之间笛卡尔坐标的差值线性变化，并已通过B3LYP/6 - 311G（）计算得到验证。在预测极化率各向异性的情况下，已表明对应于体相原子极化率80%的类似原子极化率适合重现B3LYP结果，而纳入电荷转移效应可略微改善一致性，前提是电荷转移量随团簇尺寸增加。
