Decisive role of nuclear quantum effects on surface mediated water dissociation at finite temperature.
Decisive role of nuclear quantum effects on surface mediated water dissociation at finite temperature.
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DOI：
10.1063/1.5002537
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发表时间：
2017-10
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影响因子：
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通讯作者：
Y. Litman;D. Donadio;M. Ceriotti;M. Rossi
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文献类型：
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作者：
Y. Litman;D. Donadio;M. Ceriotti;M. Rossi
水分子吸附在无机基质上，在许多技术应用中起着重要作用。在吸附剂中存在光原子时，核量子效应（NQEs）影响这些系统的结构稳定性和动力学性质。在这项工作中，我们探讨了NQEs对阶梯Pt（221）表面上水丝解离的影响。通过使用范德华校正密度泛函理论进行从头算分子动力学模拟，我们注意到，在有限温度下，完整结构和解离结构的几个相互竞争的最小值都是可以获得的，这使得评估量子自由能的谐波估计是否足以确定不同状态的相对稳定性变得重要。因此，我们执行从头算路径积分分子动力学（PIMD），以便在考虑有限温度下的构象熵和非谐性的情况下计算这些贡献。我们提出，当吸附较弱且基材上的NQEs可以忽略不计时，可以通过对系统的简单划分进行PIMD模拟，从而节省大量计算量。然后我们计算nqe对自由能的全部贡献，也包括非调和项。我们发现，与谐波估计相比，它们导致离解自由能的量子贡献增加了高达20%。我们还发现，离解过程的贡献可以忽略不计，但由零点能量主导，这可以将离解速率提高三个数量级。最后，我们强调了温度和NQEs如何间接影响偶极子和电子密度的再分布，导致相对于静态估计的功函数变化高达0.4 eV。这种功函数变化的定量测定提供了一种可能的方法，可以通过实验确定阶梯表面上水低聚物的最稳定构型。
Water molecules adsorbed on inorganic substrates play an important role in several technological applications. In the presence of light atoms in adsorbates, nuclear quantum effects (NQEs) influence the structural stability and the dynamical properties of these systems. In this work, we explore the impact of NQEs on the dissociation of water wires on stepped Pt(221) surfaces. By performing ab initio molecular dynamics simulations with van der Waals corrected density functional theory, we note that several competing minima for both intact and dissociated structures are accessible at finite temperatures, making it important to assess whether harmonic estimates of the quantum free energy are sufficient to determine the relative stability of the different states. We thus perform ab initio path integral molecular dynamics (PIMD) in order to calculate these contributions taking into account the conformational entropy and anharmonicities at finite temperatures. We propose that when adsorption is weak and NQEs on the substrate are negligible, PIMD simulations can be performed through a simple partition of the system, resulting in considerable computational savings. We then calculate the full contribution of NQEs to the free energies, including also anharmonic terms. We find that they result in an increase of up to 20% of the quantum contribution to the dissociation free energy compared with the harmonic estimates. We also find that the dissociation process has a negligible contribution from tunneling but is dominated by zero point energies, which can enhance the rate of dissociation by three orders of magnitude. Finally we highlight how both temperature and NQEs indirectly impact dipoles and the redistribution of electron density, causing work function changes of up to 0.4 eV with respect to static estimates. This quantitative determination of the change in the work function provides a possible approach to determine experimentally the most stable configurations of water oligomers on the stepped surfaces.