Tribology at the atomic scale with density functional theory

Abstract

Understanding the quantum mechanical origins of friction forces has become increasingly important in the past decades with the advent of nanotechnology. At the nanometer scale, the universal Amontons-Coulomb laws cease to be valid and each interface requires individual scrutiny. Furthermore, measurements required to understand friction at the atomic scale are riddled with artificial factors such as the properties of the friction force microscope, effect of the environment, and the type of the substrate. It therefore proves difficult to isolate the actual behavior of interfaces from these effects. Electronic structure methods are an indispensible tool in understanding the details of interfaces, their interactions with lubricants, the environment and the support. In particular, density functional theory (DFT) has given large contributions to the field through accurate calculations of important properties such as the potential energy surfaces, shear strengths, adsorption of lubricant materials and the effect of the substrate. Although unable to tackle velocity- or temperature-dependent properties for which classical molecular dynamics is employed, DFT provides an affordable yet accurate means of understanding the quantum mechanical origins of the tribological behavior of interfaces in a parameter-free manner. This review attempts to give an overview of the ever-increasing literature on the use of DFT in the field of tribology. We start by summarizing the rich history of theoretical work on dry friction. We then identify the figures-of-merit which can be calculated using DFT. We follow by a summary of bulk interfaces and how to reduce friction via passivation and lubricants. The following section, namely friction involving two-dimensional materials is the focus of our review since these materials have gained increasing traction in the field thanks to the advanced manifacturing and manipulation techniques developed. Our review concludes with a brief touch on other interesting examples from DFT tribology literature such as rolling friction and the effect of photoexcitation in tribology.

A Classical Molecular Dynamics Study of the Effect of the Atomic Force Microscope Tip Shape, Size and Deformation on the Tribological Properties of the Graphene/Au(111) Interface

“…This is also seen to a certain extent for the cone but is much more pronounced for the hemisphere. In an actual sliding experiment, the stick-slip occurs due to both the elastic properties of the tip and the substrate [7], whereas in the present case of rigid tips, we only observe the effect of the substrates. At T = 100 K, the periodic structure of the lateral force with well-defined peaks is mostly lost for the cone and the hemisphere for sliding along the x direction due to increased thermal motion of the atoms.…”

“…This function enables the understanding and identification of low-friction interfaces and lubricants. For instance, in recent years, two-dimensional materials have emerged as excellent lubricants with very low friction [6][7][8][9].…”

Insights into modeling approaches for boundary- and mixed-lubricated conditions

“…DFT can predict the chemical reactions, including reaction pathways, energy barriers and the stability of reaction products, which occur at sliding surfaces, which are often responsible for wear and material degradation. DFT simulations can shed light on the formation, composition and stability of tribofilms, thus gaining a deeper understanding how these protective layers are formed and attached to the underlying substrates in Figure 3 (Ta et al , 2021; Shenghua et al , 2003; Ustunel and Toffoli, 2022).…”

Friction properties of black phosphorus: a first-principles study

“…Theoretically, anisotropic friction and superlubricity behaviors of BP have been investigated by molecular dynamics simulations [46][47][48][49][50]. Moreover, density functional theory (DFT) is an indispensable tool to study the mechanism of friction, wear and lubrication, and has made great contributions to the tribology field by accurately calculating the potential energy surface, shear strength, charge transfer between friction pairs, etc [51]. Recently, structural superlubricity in phosphorene has been identified by means of DFT calculations [52].…”