Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, People's Republic of China.
J Chem Phys. 2012 Jun 14;136(22):224304. doi: 10.1063/1.4726124.
Based on first-principles calculations, a decomposition scheme is proposed to investigate the molecular site-specific first-order hyperpolarizability (β) responses by means of Hirshfeld population analysis and finite field method. For a molecule, its β is decomposed into local and nonlocal contributions of individual atoms or groups. The former describes the response within the atomic sphere, while the latter describes the contributions from interatomic charge transfer. This scheme is then applied to six prototypical donor-acceptor (D-A) or D-π-A molecules for which the local and nonlocal hyperpolarizabilities are evaluated based on their MP2 density. Both the local and nonlocal parts exhibit site-specific characteristics, but vary differently with molecular structures. The local part depends mainly on the atomic attributes such as electronegativity and charge state, as well as its location in the molecule, while the nonlocal part relates to the ability and distance of charge delocalization within the molecule, increasing rapidly with molecular size. The proposed decomposition scheme provides a way to distinguish atomic or group contributions to molecular hyperpolarizabilities, which is useful in the molecular design for organic nonlinear optical materials.
基于第一性原理计算，提出了一种分解方案，通过 Hirshfeld 布居分析和有限场方法研究分子的特定位置一阶超极化率（β）响应。对于一个分子，其β可以分解为单个原子或基团的局部和非局部贡献。前者描述了原子球内的响应，而后者描述了原子间电荷转移的贡献。然后，该方案应用于六个典型的给体-受体（D-A）或 D-π-A 分子，根据其 MP2 密度评估了局部和非局部超极化率。局部和非局部部分都表现出特定位置的特征，但随分子结构的变化而不同。局部部分主要取决于原子属性，如电负性和电荷状态，以及其在分子中的位置，而非局部部分与分子内电荷离域的能力和距离有关，随分子尺寸的增加而迅速增加。所提出的分解方案提供了一种区分分子超极化率中原子或基团贡献的方法，这对于有机非线性光学材料的分子设计非常有用。
