Theory and method for calculating resonance Raman scattering from resonance polarizability derivatives.
Theory and method for calculating resonance Raman scattering from resonance polarizability derivatives.
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DOI：
10.1063/1.2046670
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发表时间：
2005-11
期刊：
影响因子：
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通讯作者：
L. Jensen;L. Zhao;J. Autschbach;G. Schatz
中科院分区：
文献类型：
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作者：
L. Jensen;L. Zhao;J. Autschbach;G. Schatz
我们提出了一种从频率相关极化率的几何导数计算正法拉曼散射（NRS）和共振拉曼散射（RRS）光谱的方法。在RRS的情况下，极化导数是通过包含电子激发态的有限寿命，利用时变密度泛函理论从共振极化计算得到的。这种方法是克雷默、海森堡和狄拉克形式主义的短期近似。当只考虑一个电子激发态时，它与简单的激发态梯度近似法类似，但它并不局限于只考虑一个电子激发态。由于该方法可以应用于NRS和RRS，因此可以获得完整的拉曼激励曲线。为了验证这一方法，我们给出了尿嘧啶的S2态和芘的S4、S3和S2态的结果。结果与激发态梯度近似法的结果基本一致。与实验结果比较，我们发现总体上有很好的一致性，可以将实验波段分配到计算光谱中的波段。对于尿嘧啶，在计算中加入显水是与溶液光谱相匹配的必要条件。计算得到的共振增强数量级为10(4)-10(6)，与实验结果一致。对于芘，该方法还能够区分实验数据可用的三种不同的电子态。计算中忽略了非调和性和溶剂效应，导致理论与实验存在一定的出入。
We present a method to calculate both normal Raman-scattering (NRS) and resonance Raman-scattering (RRS) spectra from the geometrical derivatives of the frequency-dependent polarizability. In the RRS case, the polarizability derivatives are calculated from resonance polarizabilities by including a finite lifetime of the electronic excited states using time-dependent density-functional theory. The method is a short-time approximation to the Kramers, Heisenberg, and Dirac formalism. It is similar to the simple excited-state gradient approximation method if only one electronic excited state is important, however, it is not restricted to only one electronic excited state. Since the method can be applied to both NRS and RRS, it can be used to obtain complete Raman excitation profiles. To test the method we present the results for the S2 state of uracil and the S4, S3, and S2 states of pyrene. As expected, the results are almost identical to the results obtained from the excited-state gradient approximation method. Comparing with the experimental results, we find in general quite good agreement which enables an assignment of the experimental bands to bands in the calculated spectrum. For uracil the inclusion of explicit waters in the calculations was found to be necessary to match the solution spectra. The calculated resonance enhancements are on the order of 10(4)-10(6), which is in agreement with experimental findings. For pyrene the method is also able to distinguish between the three different electronic states for which experimental data are available. The neglect of anharmonicity and solvent effects in the calculations leads to some discrepancy between theory and experiment.