Definition and detection of contact in atomistic simulations

In atomistic simulations, contact depends on the accurate detection of contacting atoms as well as their contact area. While it is common to define contact between atoms based on the so-called 'contact distance' where the interatomic potential energy reaches its minimum, this discounts, for example, temperature effects on atomic vibrations and, correspondingly, the spatial distributions of atoms. In the present study, classical molecular dynamics was used to investigate the definition and detection of contact between a spherical particle (made of either silver, lead, or platinum) and a flat substrate (silver). Total contact areas are estimated via three previously published methods for the detection of atoms in contact: the first method detects contacting atoms based on their potential energy values; the second method utilizes interatomic distances; and, the last method is based on the interacting potential energy values between the contacting atoms of the counterpart surfaces. Each method is examined in detail with our findings suggesting that the use of interatomic distances is the most suitable way to define and detect the real area of contact in atomistic simulations of normal contact. Our results suggest that the minimum of the radial distribution function after the first peak can be defined as the contact distance. Also, a temperature-dependent empirical equation is proposed to estimate the contact distance for Lennard-Jones-type potentials. Moreover, the atomic diameter is defined as the distance between the origin (i.e. the center of the reference atom) and the first peak in the radial distribution function, allowing for an estimation of the atomic contact area. (C) 2015 Elsevier B.V. All rights reserved.