A
study on how gold atoms bond to other atoms using a model that takes
into account bonds direction has been carried out by physicist Marie
Backman from the University of Helsinki, Finland, and colleagues. These
findings, which are about to be published in EPJ B, are 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 authors 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 authors
used theoretical and computational analysis to study gold atoms
interacting with their neighbours. 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, for example, involve
the development of cross potentials for gold nanoparticles and nanorods
in a matrix, typically used in biomedical imaging and nanophotonics.
Unravelling gold’s bonding mysteries
Source: Springer
