Chen Wei, Li Zhi-Ru, Wu Di, Li Rui-Yan, Sun Chia-Chung
State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Jiefang Road 119, Changchun 130023, PR China.
J Phys Chem B. 2005 Jan 13;109(1):601-8. doi: 10.1021/jp0480394.
Two new classes of (HCN)(n)...Li and Li...(HCN)(n) (n = 1, 2, 3) clusters with the electride characteristic are formed in theory by the metal Li atom attaching to the (HCN)(n) (n = 1, 2, 3) clusters. Because of the interaction between the Li atom and the (HCN)(n) part, the 2s valence electron of the Li atom becomes a loosely bound excess electron. Our high-level ab initio calculations show that these new clusters with the excess electron have large first hyperpolarizabilities, for example, beta(0) = -15,258 au for (HCN)...Li and beta(0) = -3401 au for Li...(HCN) at the QCISD/6-311++G(3df,3pd) level (only beta(0) = -2.8 au for HCN monomer(26)). Obviously, the excess electron from the Li atom plays a crucial role in the large first hyperpolarizabilities of these clusters. The beta(0) value of (HCN)(n)...Li (beta(0) > 10(4) au, from sigma --> pi* transition) is larger than that of Li...(HCN)(n) (beta(0) > 10(3) au, from sigma --> sigma* transition) for n = 1, 2, or 3. In addition, two interesting rules have been observed. They are that |beta(0)| decreases with lengthening of the HCN chain for (HCN)(n)...Li clusters and that |beta(0)| increases as n increases for Li...(HCN)(n) clusters. In this paper, we discuss two classes of clusters that are highly similar to the electride structure model, of which the structural characteristics are that alkali metal atoms ionize to form cations and trapped electrons under the action of other polar molecules. Thus, the investigation on the large first hyperpolarizabilities of (HCN)(n)...Li and Li...(HCN)(n) (n = 1, 2, 3) may prompt one to study the unusual nonlinear optical responses of some electrides.
通过金属锂原子附着于(HCN)ₙ（n = 1, 2, 3）团簇，理论上形成了两类具有电子化物特性的(HCN)ₙ...Li和Li...(HCN)ₙ（n = 1, 2, 3）团簇。由于锂原子与(HCN)ₙ部分之间的相互作用，锂原子的2s价电子成为一个束缚松散的多余电子。我们的高精度从头算计算表明，这些带有多余电子的新团簇具有较大的第一超极化率，例如，在QCISD/6 - 311++G(3df,3pd)水平下，(HCN)...Li的β(0) = -15258 au，Li...(HCN)的β(0) = -3401 au（HCN单体的β(0)仅为 -2.8 au(26)）。显然，来自锂原子的多余电子在这些团簇的大第一超极化率中起着关键作用。对于n = 1、2或3，(HCN)ₙ...Li的β(0)值（β(0) > 10⁴ au，源于σ→π跃迁）大于Li...(HCN)ₙ的β(0)值（β(0) > 10³ au，源于σ→σ跃迁）。此外，还观察到两条有趣的规律。它们是，对于(HCN)ₙ...Li团簇，|β(0)|随着HCN链的延长而减小；对于Li...(HCN)ₙ团簇，|β(0)|随着n的增加而增大。在本文中，我们讨论了两类与电子化物结构模型高度相似的团簇，其结构特征是碱金属原子在其他极性分子的作用下电离形成阳离子并俘获电子。因此，对(HCN)ₙ...Li和Li...(HCN)ₙ（n = 1, 2, 3）的大第一超极化率的研究可能促使人们去研究一些电子化物异常的非线性光学响应。
