Lanzi Cecilia, Aieta Chiara, Ceotto Michele, Conte Riccardo
Dipartimento di Chimica, Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy.
J Chem Phys. 2024 Jun 7;160(21). doi: 10.1063/5.0214037.
We propose a new semiclassical approach to the calculation of molecular IR spectra. The method employs the time averaging technique of Kaledin and Miller upon symmetrization of the quantum dipole-dipole autocorrelation function. Spectra at high and low temperatures are investigated. In the first case, we are able to point out the possible presence of hot bands in the molecular absorption line shape. In the second case, we are able to reproduce accurate IR spectra as demonstrated by a calculation of the IR spectrum of the water molecule, which is within 4% of the exact intensity. Our time averaged IR spectra can be directly compared to time averaged semiclassical power spectra as shown in an application to the CO2 molecule, which points out the differences between IR and power spectra and demonstrates that our new approach can identify active IR transitions correctly. Overall, the method features excellent accuracy in calculating absorption intensities and provides estimates for the frequencies of vibrations in agreement with the corresponding power spectra. In perspective, this work opens up the possibility to interface the new method with the semiclassical techniques developed for power spectra, such as the divide-and-conquer one, to get accurate IR spectra of complex and high-dimensional molecular systems.
我们提出了一种计算分子红外光谱的新半经典方法。该方法在量子偶极 - 偶极自相关函数对称化后采用了卡列丁和米勒的时间平均技术。研究了高温和低温下的光谱。在第一种情况下，我们能够指出分子吸收线形中可能存在的热谱带。在第二种情况下，通过对水分子红外光谱的计算表明，我们能够重现精确的红外光谱，其强度与精确值相差在4%以内。我们的时间平均红外光谱可以直接与时间平均半经典功率谱进行比较，如在二氧化碳分子的应用中所示，这指出了红外光谱和功率谱之间的差异，并表明我们的新方法能够正确识别活跃的红外跃迁。总体而言，该方法在计算吸收强度方面具有出色的准确性，并能提供与相应功率谱一致的振动频率估计。从长远来看，这项工作为将新方法与为功率谱开发的半经典技术（如分治法）相结合以获得复杂高维分子系统的精确红外光谱开辟了可能性。
