Development of atomistic MEAM potentials for the silicon-oxygen-gold ternary system

In this paper, we present a scheme for the development of Si-O, O-O and Au-O modified embedded atom method (MEAM) potential models which can be combined with previously developed Si-Si, Au-Si and Au-Au MEAM potential functions to describe the structural properties of the Au-silica interface as well as several important polymorphs of crystalline silica: alpha- and beta-quartz alpha- and beta-cristobalite and beta-tridymite. Longer-ranged interactions (beyond first nearest neighbour) must be included to stabilize crystalline silica structures. The challenge of finding an appropriate reference structure for this diversely bonded system was solved using the dimer, rather than any single crystalline form of silica, as the reference structure. For the Si-O and O-O potentials, the ground state properties of the reference structures were calculated using DFT calculations and the remaining parameters fitted to the structural properties of alpha-quartz. For the Au-O potential, the parameters were fitted to the bond lengths, the twisted bond angle and the binding energy of a Au atom bound to a SiO4 cluster. The reliability and transferability of this newly developed MEAM potential model for silica have been examined through a series of validations, such as a dynamic stability test using molecular dynamics (MD) simulations and predictions of optimal structural parameters. bulk modulus and binding energies of several important polymorphs of crystalline silica. For the validation of the Au-O MEAM potential, we calculated adsorption energies and bond lengths of a Au adatom on various sites of an alpha-quartz slab using the MEAM potentials and DFT calculations. The agglomeration behaviour and contact angle of a gold island deposited on a silica substrate were examined using MID simulations and found to compare satisfactorily with the experiment. The quality of the models is noteworthy given that our study constitutes a feasibility evaluation of the capability of the MEAM formalism to represent a system which contains the characteristics of both covalent and ionic bonding.