Bauerhenne Bernd, Lipp Vladimir P, Zier Tobias, Zijlstra Eeuwe S, Garcia Martin E
Theoretical Physics and Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel, Heinrich-Plett-Straße 40, 34132 Kassel, Germany.
Center for Free-Electron Laser Science CFEL, Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany.
Phys Rev Lett. 2020 Feb 28;124(8):085501. doi: 10.1103/PhysRevLett.124.085501.
Large-scale simulations using interatomic potentials provide deep insight into the processes occurring in solids subject to external perturbations. The atomistic description of laser-induced ultrafast nonthermal phenomena, however, constitutes a particularly difficult case and has so far not been possible on experimentally accessible length scales and timescales because of two main reasons: (i) ab initio simulations are restricted to a very small number of atoms and ultrashort times and (ii) simulations relying on electronic temperature- (T_{e}) dependent interatomic potentials do not reach the necessary ab initio accuracy. Here we develop a self-learning method for constructing T_{e}-dependent interatomic potentials which permit ultralarge-scale atomistic simulations of systems suddenly brought to extreme nonthermal states with density-functional theory (DFT) accuracy. The method always finds the global minimum in the parameter space. We derive a highly accurate analytical T_{e}-dependent interatomic potential Φ(T_{e}) for silicon that yields a remarkably good description of laser-excited and -unexcited Si bulk and Si films. Using Φ(T_{e}) we simulate the laser excitation of Si nanoparticles and find strong damping of their breathing modes due to nonthermal melting.
使用原子间势进行的大规模模拟为深入了解受外部扰动的固体中发生的过程提供了深刻见解。然而，激光诱导的超快非热现象的原子描述是一个特别困难的情况，由于两个主要原因，迄今为止在实验可及的长度和时间尺度上还无法实现：（i）从头算模拟仅限于极少数原子和超短时间，（ii）依赖于电子温度（(T_{e})）的原子间势的模拟无法达到必要的从头算精度。在此，我们开发了一种自学习方法来构建依赖于(T_{e})的原子间势，该势允许以密度泛函理论（DFT）精度对突然进入极端非热状态的系统进行超大尺度原子模拟。该方法总能在参数空间中找到全局最小值。我们推导了一种用于硅的高度精确的解析依赖于(T_{e})的原子间势(\varPhi(T_{e}))，它对激光激发和未激发的硅块体及硅薄膜给出了非常好的描述。使用(\varPhi(T_{e}))，我们模拟了硅纳米颗粒的激光激发，并发现由于非热熔解，其呼吸模式有强烈阻尼。
