Carbonnière P, Erba A, Richter F, Dovesi R, Rerat M
IPREM, Université de Pau et des Pays de l'Adour, IPREM-CAPT UMR CNRS 5254, Hélioparc Pau Pyrénées, 2 avenue du Président Angot, 64053 Pau Cedex 09, Pau, France.
Dipartimento di Chimica, Università di Torino, via Giuria 5, 10125 Torino, Italy.
J Chem Theory Comput. 2020 May 12;16(5):3343-3351. doi: 10.1021/acs.jctc.9b01061. Epub 2020 Apr 28.
An extension of the CRYSTAL program is presented allowing for calculations of anharmonic infrared (IR) intensities and Raman activities for periodic systems. This work is a follow-up of two papers devoted to the computation of anharmonic vibrational states of solids from DFT (density functional theory) calculations (Erba et al. 2019, 15, 3755-3765 and Erba et al. 2019, 15, 3766-3777). The approach presented here relies on the evaluation of integrals of the dipole moment and polarizability operators over anharmonic wave functions obtained from either VSCF (vibrational self-consistent field) or VCI (vibrational configuration interaction) calculations. With this extension, the program now allows for a more complete characterization of the vibrational spectroscopic features of solids within the density functional theory. In particular, it is able (i) to provide reliable positions and intensities for the most intense spectral features and (ii) to check whether a first overtone or a combination band has a nonvanishing IR intensity or Raman activity. Therefore, it becomes possible to assign the transition(s) corresponding to satellite peak(s) around a fundamental transition or the overtones or combination bands that may be as intense as their corresponding fundamental transitions through the strongest mode-mode couplings, as in so-called Fermi resonances. The present method is assessed on two molecular systems, HO and HCO, as well as on two solid state cases, boron hydrides BH and their deuterated species BD in a crystalline environment of alkali metals (M = Na, K). The solid state cases are particularly insightful as, in the B-H (or B-D) stretching region here considered, they exhibit many spectral features entirely due to anharmonic effects: two out of three in the IR spectrum and four out of six in the Raman spectrum. All IR and Raman active overtones and combination bands experimentally observed are correctly predicted with our approach. The effect of the adopted quantum-chemical model (DFT exchange-correlation functional/basis set) for the electronic structure calculations on the computed spectra is discussed and found to be significant, which suggests some special care is needed for the analysis of subtle spectral features.
本文介绍了CRYSTAL程序的一个扩展，该扩展允许计算周期性系统的非谐红外（IR）强度和拉曼活性。这项工作是两篇致力于从密度泛函理论（DFT）计算固体非谐振动态的论文的后续研究（Erba等人，2019年，15卷，3755 - 3765页和Erba等人，2019年，15卷，3766 - 3777页）。这里提出的方法依赖于偶极矩和极化率算符在从VSCF（振动自洽场）或VCI（振动组态相互作用）计算得到的非谐波函数上的积分评估。通过这个扩展，该程序现在能够在密度泛函理论范围内更完整地表征固体的振动光谱特征。特别是，它能够（i）为最强的光谱特征提供可靠的位置和强度，以及（ii）检查第一泛音或组合带是否具有非零的红外强度或拉曼活性。因此，通过最强的模式 - 模式耦合，就有可能确定与基频跃迁周围的卫星峰相对应的跃迁，或者确定泛音或组合带，这些泛音或组合带可能与它们相应的基频跃迁一样强，就像在所谓的费米共振中那样。本方法在两个分子体系HO和HCO以及两个固态案例上进行了评估，这两个固态案例是碱金属（M = Na，K）晶体环境中的硼氢化物BH及其氘代物种BD。固态案例特别具有启发性，因为在这里考虑的B - H（或B - D）伸缩区域中，它们表现出许多完全归因于非谐效应的光谱特征：红外光谱中有三分之二，拉曼光谱中有六分之四。我们的方法正确地预测了所有实验观察到的红外和拉曼活性泛音和组合带。讨论了用于电子结构计算的所采用的量子化学模型（DFT交换 - 相关泛函/基组）对计算光谱的影响，并发现其影响显著，这表明在分析微妙的光谱特征时需要格外小心。
