New Model to Explain How Gold Binds to Other Materials

An international team of scientists has used a new empirical model to explore how gold atoms bond to other atoms.

Gold crystals (Alchemist-hp, www.pse-mendelejew.de / CC BY-SA 3.0)

The study, published in the European Physical Journal B: Condensed Matter and Complex Systems, is a first step toward better understanding how gold binds to other materials through strong, so-called covalent, bonds.

What scientists need is an empirical model based on a so-called potential that describes the gold-gold bond in a reliable way. Most previous models only accounted for interactions in the spherical electron density around the atom. Although it is suitable to describe bonds between gold atom pairs, it is not adequate to describe how surface gold atoms bond to other materials. In such a case, the density of interacting electrons is no longer spherical.

Indeed, bond angles matter when gold binds to other materials. Thus, the team led by Dr Marie Backman of the University of Helsinki, Finland, used a model based on potentials with angular dependence, referred to as Tersoff potential. It offers a compromise between including bond directionality, which is needed for covalent bonds, and keeping the computer time needed for the simulations low.

The scientists used theoretical and computational analysis to study gold atoms interacting with their neighbors. They fitted their potential functions to the most important observed characteristics of gold, such as gold atoms’ lattice constant, binding energy and elastic constants.

Thanks to such potential functions they were then able to describe bonding in atomistic simulations.
This involves, first, determining the forces on each atom based on their relative positions and second solving equations of motion, to show how the atoms move, on a very short time scale.

Building on this model, future work could involve the development of cross potentials for gold nanoparticles and nanorods in a matrix, typically used in biomedical imaging and nanophotonics.

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Bibliographic information: M. Backman et al. 2012. Bond order potential for gold. European Physical Journal B, vol. 85, no. 9, 317; doi: 10.1140/epjb/e2012-30429-y