Hollas Daniel, Muchová Eva, Slavíček Petr
Department of Physical Chemistry, University of Chemistry and Technology Prague, Technická 5, 16628 Prague 6, Czech Republic.
J Chem Theory Comput. 2016 Oct 11;12(10):5009-5017. doi: 10.1021/acs.jctc.6b00630. Epub 2016 Oct 3.
We present a computational protocol for modeling valence photoemission spectra of liquids. We use water as an experimentally well-characterized model system, and we represent its liquid state by larger finite-sized droplets. The photoemission spectrum is evaluated for an ensemble of structures along molecular dynamics simulations. The nuclear quantum effects are accounted for by based path-integral molecular dynamics simulations that are greatly accelerated with the so-called colored noise thermostat (PI+GLE) method. The ionization energies for the valence electrons are evaluated as orbital energies of optimally tuned range-separated hybrid functionals (OT-RSH). This approach provides Koopmans-type ionization energies including relaxation energy. We show that the present protocol can quantitatively describe the valence photoemission spectrum of liquid water, i.e., the positions, shapes, and widths of the photoemission peaks. With the PI+GLE simulations, even the subtle isotope effects that have been recently observed experimentally can be modeled. The electronic properties of finite-sized droplets are shown to converge rapidly to those of liquids. We discuss the importance of proper tuning of the range-separation parameter in OT-RSH as well as possible sources of error in our simulations. The present approach seems to be a viable route to modeling photoemission spectra of liquids, especially in conjunction with efficient implementation of density functional methods on graphical processing units.
我们提出了一种用于模拟液体价带光电子能谱的计算协议。我们将水作为一个实验上特征明确的模型系统，并通过更大的有限尺寸液滴来表示其液态。沿着分子动力学模拟，对一组结构的光电子能谱进行评估。通过基于路径积分分子动力学模拟来考虑核量子效应，该模拟通过所谓的彩色噪声恒温器（PI + GLE）方法得到了极大加速。价电子的电离能被评估为最优调整的范围分离混合泛函（OT - RSH）的轨道能量。这种方法提供了包括弛豫能在内的库普曼斯型电离能。我们表明，本协议能够定量描述液态水的价带光电子能谱，即光电子能谱峰的位置、形状和宽度。通过PI + GLE模拟，甚至最近实验观测到的微妙同位素效应也能够被模拟。有限尺寸液滴的电子性质被证明能迅速收敛到液体的性质。我们讨论了在OT - RSH中适当调整范围分离参数的重要性以及我们模拟中可能的误差来源。本方法似乎是模拟液体光电子能谱的一条可行途径，特别是结合在图形处理单元上高效实现密度泛函方法时。
