Building the bridge from atomistic to stochastic modelling of nanoscale friction phenomena

搭建纳米级摩擦现象从原子建模到随机建模的桥梁

• 批准号: RGPIN-2015-04486
• 负责人: Evstigneev, Mykhaylo
• 金额: $ 1.6万
• 依托单位: Memorial University of Newfoundland
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=650361
• 关键词: Building; bridge; atomistic; stochastic; modelling

Direct molecular dynamic simulation of a nanoscale object involves numerical integration of the equations of motion for all its atoms. This approach is exact, but it has severe size and time-scale limitations. Stochastic modelling overcomes these limitations by focusing on only a small subset of the relevant degrees of freedom, termed "the system". The remaining large number of the irrelevant ones, denoted as "the heat bath", are not simulated explicitly, but taken into account by (i) renormalizing the forces acting on and between the system coordinates, (ii) including dissipative forces describing the energy transfer from the system into the heat bath, and (iii) introducing random forces describing the effect of thermal motion of the heat-bath atoms on the system.  ***Stochastic modelling requires approximative assumptions, and thus it is not always clear how to correctly incorporate the heat-bath effects (i)-(iii) into the system's equations of motion. The goal of this program is to work out the rules allowing one to obtain the ingredients (i)-(iii) from the knowledge of the forces acting between the system and the bath atoms. The second goal is to apply these rules to study the dynamics of nanoscale objects, such as single atoms, atomic clusters, and nanoparticles in contact with a solid surface.***An important nanoscale object is the tip of an atomic force microscope, a standard experimental tool used for surface analysis. Its application particularly pertinent to this program is the study of friction phenomena at the nanoscale. While macroscopic friction results from complex interaction between many asperities on the two surfaces in contact, the newly emerging research field of nanotribology is focused on the interaction of a single such asperity - the atomic force microscope tip - with an atomically flat surface. The common feature of macro- and nanoscale friction is that both exhibit the phenomenon of aging, that is, gradual increase of friction force with contact duration. While aging in the macroscopic friction has been investigated for several decades, its nanoscale counterpart was first established experimentally less than a decade ago. ***Nanoscale friction has been studied theoretically using stochastic modelling, but the majority of such models do not consider the possibility of contact aging. The further goal of the present program is to improve the existing stochastic models of nanoscale friction by including the effect of aging of the tip-substrate contact.***The*anticipated outcome of this program is improvement of our understanding of the laws of nature acting at the nanoscale, and development of efficient numerical*tools to simulate the dynamics of nanoscale objects on solid surfaces. These tools should find a number of scientific and technological applications in such fields as manipulation of nanoparticles, investigation of their interactions, and control of friction.**

对纳米尺度物体的直接分子动力学模拟包括对其所有原子的运动方程进行数值积分。这种方法是精确的，但它有严重的大小和时间尺度限制。随机建模克服了这些限制，只关注相关自由度的一个小子集，被称为“系统”。剩下的大量不相关的模型，称为“热浴”，没有被显式地模拟，但通过(I)使作用在系统坐标上和系统坐标之间的力重新正规化，(Ii)包括描述从系统到热浴的能量转移的耗散力，以及(Iii)引入描述热浴原子的热运动对系统的影响的随机力。*随机建模需要近似的假设，因此并不总是清楚如何正确地将热浴效应(I)-(Iii)合并到系统的运动方程中。这个计划的目标是制定规则，允许人们从系统和浴原子之间的作用力的知识中获得成分(I)-(Iii)。第二个目标是应用这些规则来研究纳米级物体的动力学，如单原子、原子团和与固体表面接触的纳米颗粒。*一个非常重要的纳米级物体是原子力显微镜的尖端，这是用于表面分析的一种非常标准的实验工具。与该计划特别相关的应用是在纳米尺度上研究摩擦现象。虽然宏观摩擦是由于接触的两个表面上的许多粗糙度之间的复杂相互作用而产生的，但新兴的纳米摩擦学研究领域主要集中在单个这样的粗糙度--原子力显微镜和尖端--与原子平坦表面的相互作用。宏观和纳米尺度摩擦的共同特征是都表现出老化现象，即摩擦力随着接触时间的延长而逐渐增加。虽然宏观摩擦中的老化已经被研究了几十年，但它在纳米尺度上的对应关系是在不到十年前首次通过实验建立的。*已经使用随机模型从理论上研究了纳米级摩擦，但大多数此类模型没有考虑接触老化的可能性。本计划的进一步目标是通过包括针尖-基片接触老化的影响来改进现有的纳米级摩擦的随机模型。*该计划的预期结果是提高我们对纳米级自然作用规律的理解，并开发有效的数值*工具来模拟纳米级物体在固体表面上的动力学。这些工具应该在操纵纳米粒子、研究它们的相互作用和控制摩擦等领域找到一些科学和技术应用。