Vibrational response and motion of carbon monoxide on Cu(100) driven by femtosecond laser pulses: Molecular dynamics with electronic friction
Vibrational response and motion of carbon monoxide on Cu(100) driven by femtosecond laser pulses: Molecular dynamics with electronic friction
复制标题
DOI：
10.1103/physrevb.100.245431
复制
发表时间：
2019-12-26
影响因子：
3.7
通讯作者：
Saalfrank, Peter
中科院分区：
文献类型：
--
作者：
Scholz, Robert;Lindner, Steven;Saalfrank, Peter
铜表面上的一氧化碳仍然是一个迷人的、丰富的微实验室，可以解决表面科学中不断演变的许多问题。最近，热电子介导的飞秒激光脉冲诱导CO分子在铜(100)面上的动力学成为实验的焦点[井上等人，物理。莱特牧师。186101(2016年)]和理论[Novko等人，Phys.莱特牧师。122,016806(2019年)]，揭开了超短(亚皮秒)时间尺度上振动非平衡动力学的细节。本文用带电子摩擦的分子动力学(MDEF)方法研究了全维热电子驱动的时间分辨动力学。在描述分子自由度与铜表面电子-空穴对耦合的朗之万方程中包含了耗散项，该方程由梯度修正的密度泛函理论(DFT)通过局域密度摩擦近似(LDFA)计算。推广的朗之万振子模型考虑了表面声子引起的弛豫。热电子诱导激发用含时电子温度描述，后者由改进的双温模型导出。我们在预先计算的势能面上的无参数模拟允许很好的统计，观察到的趋势被带有电子摩擦的即时从头计算分子动力学(AIMDEF)计算所证实。通过计算特定分子振动的时间分辨频率图、瞬时频率、概率分布和关联函数，我们获得了对热电子驱动的动力学的微观洞察，我们可以将振动内部CO伸缩模频率的时间演化与测量数据联系起来，特别是观察到的红移。在定量上，后者在MDEF中比在实验中大，并讨论了这种观察到的可能原因。在我们的模型中，我们还观察到了大振幅低频模式的激发和时间演化、CO的横向表面扩散和分子脱附。还讨论了表面原子运动和激光注量的影响。
Carbon monoxide on copper surfaces continues to be a fascinating, rich microlab for many questions evolving in surface science. Recently, hot-electron mediated, femtosecond-laser pulse induced dynamics of CO molecules on Cu(100) were the focus of experiments [Inoue et al., Phys. Rev. Lett. 117, 186101 (2016)] and theory [Novko et al., Phys. Rev. Lett. 122, 016806 (2019)], unraveling details of the vibrational nonequilibrium dynamics on ultrashort (subpicoseconds) timescales. In the present work, full-dimensional time-resolved hot-electron driven dynamics are studied by molecular dynamics with electronic friction (MDEF). Dissipation is included by a friction term in a Langevin equation which describes the coupling of molecular degrees of freedom to electron-hole pairs in the copper surface, calculated from gradient-corrected density functional theory (DFT) via a local density friction approximation (LDFA). Relaxation due to surface phonons is included by a generalized Langevin oscillator model. The hot-electron induced excitation is described via a time-dependent electronic temperature, the latter derived from an improved two-temperature model. Our parameter-free simulations on a precomputed potential energy surface allow for excellent statistics, and the observed trends are confirmed by on-the-fly ab initio molecular dynamics with electronic friction (AIMDEF) calculations. By computing time-resolved frequency maps for selected molecular vibrations, instantaneous frequencies, probability distributions, and correlation functions, we gain microscopic insight into hot-electron driven dynamics and we can relate the time evolution of vibrational internal CO stretch-mode frequencies to measured data, notably an observed redshift. Quantitatively, the latter is found to be larger in MDEF than in experiment and possible reasons are discussed for this observation. In our model, in addition we observe the excitation and time evolution of large-amplitude low-frequency modes, lateral CO surface diffusion, and molecular desorption. Effects of surface atom motion and of the laser fluence are also discussed.