静态NLO可验证性：根据精确结果测试近似方案
Static NLO susceptibilities: testing approximation schemes against exact results
摘要：
静态光学（超）极化率的计算中通常采用的近似的可靠性测试对一个有趣的玩具模型获得的精确结果。该模型考虑了典型的非线性有机材料的主要特点，与移动电子强烈耦合到分子振动。详细分析了状态和法和有限域法中引入的近似方法。波恩-奥本海默近似和钳位核近似对分子都是安全的，而对于供体-受体电荷转移复合物，预期会偏离绝热性。在低振动频率区，势能的连续导数对静态极化率有很大的影响，振动对超极化率有很大的贡献，非谐效应对超极化率有很大的修正，线性极化率的谐波近似对非线性响应完全不适用.随着声子频率的增加，振动的作用逐渐减小，直到在反绝热（无限振动频率）状态下，振动不再对静态极化率有贡献，并且恢复了纯电子响应。
英文摘要：
The reliability of the approximations commonly adopted in the calculation of static optical (hyper)polarizabilities is tested against exact results obtained for an interesting toy-model. The model accounts for the principal features of typical nonlinear organic materials with mobile electrons strongly coupled to molecular vibrations. The approximations introduced in sum over states and finite field schemes are analyzed in detail. Both the Born-Oppenheimer and the clamped nucleus approximations turn out to be safe for molecules, whereas for donor-acceptor charge transfer complexes deviations from adiabaticity are expected. In the regime of low vibrational frequency, static susceptibilities are strongly dominated by the successive derivatives of the potential energy and large vibrational contributions to hyperpolarizabilities are found. In this regime anharmonic corrections to hyperpolarizabilities are very large, and the harmonic approximation, exact for the linear polarizability, turns out totally inadequate for nonlinear responses. With increasing phonon frequency the role of vibrations smoothly decreases, until, in the antiadiabatic (infinite vibrational frequency) regime, vibrations do not contribute anymore to static susceptibilities, and the purely electronic responses are regained.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
