Jensen L, Zhao L L, Autschbach J, Schatz G C
Northwestern University, Department of Chemistry, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
J Chem Phys. 2005 Nov 1;123(17):174110. doi: 10.1063/1.2046670.
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.
我们提出了一种从频率相关极化率的几何导数计算正常拉曼散射（NRS）和共振拉曼散射（RRS）光谱的方法。在RRS情况下，极化率导数是通过含时密度泛函理论考虑电子激发态的有限寿命，从共振极化率计算得到的。该方法是对克莱默斯、海森堡和狄拉克形式体系的一种短时近似。如果只有一个电子激发态起重要作用，它类似于简单的激发态梯度近似方法，然而，它并不局限于只有一个电子激发态。由于该方法可应用于NRS和RRS两者，所以可用于获得完整的拉曼激发轮廓。为了测试该方法，我们给出了尿嘧啶S2态以及芘S4、S3和S2态的结果。正如预期的那样，结果与从激发态梯度近似方法获得的结果几乎相同。与实验结果比较，我们发现总体上吻合得很好，这使得能够将实验谱带与计算光谱中的谱带进行归属。对于尿嘧啶，发现在计算中包含明确的水分子对于匹配溶液光谱是必要的。计算得到的共振增强因子在10(4)-10(6)量级，这与实验结果一致。对于芘，该方法也能够区分可获得实验数据的三种不同电子态。计算中忽略非谐性和溶剂效应导致理论与实验之间存在一些差异。
