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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Vibrational spectra of phosphate ions in aqueous solution probed by first-principles molecular dynamics
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Vibrational spectra of phosphate ions in aqueous solution probed by first-principles molecular dynamics

机译：第一性原理分子动力学探测水溶液中磷酸根离子的振动光谱

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摘要

We have carried out "first-principles" Born-Oppenheimer molecular dynamics (BOMD) simulations of the phosphate ions H 2PO4- and HPO42- in liquid water and have calculated their IR spectra by Fourier transform techniques from the trajectories. IR bands were assigned by a so-called "generalized normal coordinate analysis". The effects of including Hartree-Fock (HF) exchange into the density functional theory (DFT) computation of forces were studied by comparing results obtained with the well-known BP, BLYP, and B3LYP functionals. The neglect of dispersion in the functionals was empirically corrected. The inclusion of HF exchange turned out to yield dramatically improved and, thus, quite accurate descriptions of the IR spectra observed for H _2PO4- and HPO42- in aqueous solution. An analysis of earlier computational results (Kl?hn, M. et al. J. Phys. Chem. A 2004, 108, 6186-6194) on these vibrational spectra, which had been obtained in a hybrid setting combining a BP description of the respective phosphate with a simple molecular mechanics (MM) model of its aqueous environment, revealed three different sources of error, (i) the BP force field of the phosphates is much too soft and would have required a substantial scaling of frequencies, (ii) the oversimplified water force field entailed incorrect solvation structures and, thus, qualitatively wrong patterns of solvatochromic band shifts, and (iii) quantitative frequency computations additionally required the inclusion of HF exchange. Thus, the results of the B3LYP BOMD simulations do not only characterize physical properties like the IR spectra or the solvation structures of the phosphate systems but also provide clues for the future design of simplified but nevertheless reasonably accurate DFT/MM methods applicable to phosphates.
机译：我们已经对液态水中的磷酸根离子H 2PO4-和HPO42-进行了“第一性原理” Born-Oppenheimer分子动力学（BOMD）模拟，并通过傅里叶变换技术从轨迹计算了它们的IR光谱。通过所谓的“广义法向坐标分析”来分配红外波段。通过比较与众所周知的BP，BLYP和B3LYP泛函获得的结果，研究了将Hartree-Fock（HF）交换纳入力的密度泛函理论（DFT）计算中的效果。凭经验纠正了对官能团分散性的忽视。事实证明，包含HF交换可显着提高产率，因此，可以非常准确地描述水溶液中H _2PO4-和HPO42-的红外光谱。对这些振动光谱的早期计算结果（Kl？hn，M.等人，J。Phys。Chem。A 2004，108，6186-6194）的分析，是在结合了BP描述的混合设置中获得的。各自的磷酸盐具有其水溶液环境的简单分子力学（MM）模型，揭示了三种不同的误差来源，（i）磷酸盐的BP力场太软了，将需要相当大的频率缩放比例;（ii）过分简化的水力场会导致不正确的溶剂化结构，从而导致质变带变的定性模式错误;（iii）定量频率计算还需要包括HF交换。因此，B3LYP BOMD模拟的结果不仅描述了诸如红外光谱或磷酸盐系统的溶剂化结构之类的物理特性，而且还为将来简化但合理地适用于磷酸盐的DFT / MM方法设计提供了线索。

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