On the "Matsubara heating" of overtone intensities and Fermi splittings
On the "Matsubara heating" of overtone intensities and Fermi splittings
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DOI：
10.1063/5.0056829
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发表时间：
2021-09-14
影响因子：
4.4
通讯作者：
Althorpe, Stuart C.
中科院分区：
文献类型：
--
作者：
Benson, Raz L.;Althorpe, Stuart C.
经典分子动力学(MD)和虚时路径积分动力学方法通常会低估泛音和组合带的红外吸收强度一个数量级。Pple等人的研究。作者声明：[J.Chem.太棒了。155,104108(2021年)]已经证明，这是因为这些方法不能描述涨落模的质心与松原动力学的耦合；经典的一阶微扰理论(PT)应用于松原动力学，足以恢复简单模型中大部分损失的强度，并给出与量子(瑞利-薛定谔)PT相同的结果。数值结果表明，这种分析结果可以作为后处理修正因子，可应用于真实的(经典MD或路径积分动力学)红外光谱模拟。我们发现，修正因子在气相水和氨的泛音和组合带中恢复了大部分损失的强度，并为液态水恢复了大部分损失的强度。然后，我们通过将正则PT应用于松原动力学，重新推导和确认了先前的PT分析，该分析的优点是避免了长期项，并根据作用角度变量给出了受扰松原动力学的简单图景。总而言之，这些变量“松原加热”泛音和质心的组合振动的振幅，它们在经典系统中的振荡器(频率为欧米茄(I))保持在它们的量子有效温度[h欧米茄(I)coth(βh欧米茄(I)/2)/2k(B)]。数值计算表明，对“松原加热”的类似忽略导致路径积分方法低估了费米共振分裂。(C)2021年作者(S)。
Classical molecular dynamics (MD) and imaginary-time path-integral dynamics methods underestimate the infrared absorption intensities of overtone and combination bands by typically an order of magnitude. Ple et al. [J. Chem. Phys. 155, 104108 (2021)] have shown that this is because such methods fail to describe the coupling of the centroid to the Matsubara dynamics of the fluctuation modes; classical first-order perturbation theory (PT) applied to the Matsubara dynamics is sufficient to recover most of the lost intensity in simple models and gives identical results to quantum (Rayleigh-Schrodinger) PT. Here, we show numerically that the results of this analysis can be used as post-processing correction factors, which can be applied to realistic (classical MD or path-integral dynamics) simulations of infrared spectra. We find that the correction factors recover most of the lost intensity in the overtone and combination bands of gas-phase water and ammonia and much of it for liquid water. We then re-derive and confirm the earlier PT analysis by applying canonical PT to Matsubara dynamics, which has the advantage of avoiding secular terms and gives a simple picture of the perturbed Matsubara dynamics in terms of action-angle variables. Collectively, these variables "Matsubara heat" the amplitudes of the overtone and combination vibrations of the centroid to what they would be in a classical system with the oscillators (of frequency Omega(i)) held at their quantum effective temperatures [of h Omega(i) coth(beta h Omega(i)/2)/2k(B)]. Numerical calculations show that a similar neglect of "Matsubara heating" causes path-integral methods to underestimate Fermi resonance splittings. (C) 2021 Author(s).