模拟极端电子激发下固体中的时间分辨动力学
Modeling time-resolved kinetics in solids induced by extreme electronic excitation
摘要：
提出了一种并行蒙特卡罗（MC）-分子动力学（MD）方法来模拟物质对电子系统激发的响应。这两种方法在一个代码TREKIS-4中的每个时间步都在运行中组合。MC模型描述辐射的到达，在当前实现中，辐射可以由光子、电子或快离子组成。它还跟踪诱导级联激发的二次粒子，电子和空穴，以及它们的能量交换与原子由于散射。用分子动力学模型模拟了激发态原子系统。我们提出了一种简单而有效的方法来考虑共价材料中电子-原子能量转移中的非热效应，通过将系综的势能转换为原子的动能，这可以直接实现到MD模拟中。这种组合MC-MD方法使我们能够时间分辨的电子和原子系统的激发动力学的跟踪，以及它们对沉积剂量的同时响应。作为一个原理证明的例子，我们表明，所提出的方法描述了X射线照射后的原子动力学与紧束缚分子动力学的一个很好的协议，更负担得起的计算需求。新的模型也使我们能够深入了解原子系统的行为，在能量沉积过程中从一个非平衡电子系统激发的离子碰撞。
英文摘要：
We present a concurrent Monte Carlo (MC) - molecular dynamics (MD) approach to modeling of matter response to excitation of its electronic system. The two methods are combined on-the-fly at each time step in one code, TREKIS-4. The MC model describes arrival of irradiation, which in the current implementation can consist of a photon, an electron, or a fast ion. It also traces induced cascades of excitation of secondary particles, electrons and holes, and their energy exchange with atoms due to scattering. The excited atomic system is simulated with an MD model. We propose a simple and efficient way to account for nonthermal effects in the electron-atom energy transfer in covalent materials via conversion of potential energy of the ensemble into the kinetic energy of atoms, which can be straightforwardly implemented into an MD simulation. Such a combined MC-MD approach enables us time-resolved tracing of the excitation kinetics of both, electronic and atomic systems, and their simultaneous response to a deposited dose. As a proof-of-principle example, we show that proposed method describes atomic dynamics after X-ray irradiation in a good agreement with tight-binding MD, with much more affordable computational demands. The new model also allows us to gain insights into behavior of the atomic system during the energy deposition from a nonequilibrium electronic system excited by an ion impact.
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