Nanoscience research has demonstrated that gold at a size of a few nanometers or billionths of a meter may exist in the form of zigzag wires. This finding was based on computer simulations of how a few gold atoms arrange themselves in a cluster.
While the lustrous and chemically inert form of bulk gold metal continues to dominate the world of jewelry, small gold clusters consisting of few tens of atoms have unique attributes and have been much touted as potential chemical catalysts so also important components of futuristic miniature electronic and optical devices. At these miniscule size scales, the specific arrangement of atoms not only matters, rather it governs the electronic behavior of a cluster of atoms. Knowledge of the existence of zigzag arrangements of gold atoms will therefore be instrumental in the design of electronic circuitry based on these nanowires.
While experiments to resolve things at the nanometer scale are still difficult to perform, not to mention their poor accuracy and reproducibility, high-speed computation has been serving as a powerful tool for simulating the exact conditions prevalent at the nanoscale and predicting accurate results without venturing in the laboratory.
Experimentally, a nanowire consisting of a few atoms can be drawn in the laboratory by plunging the tip of a scanning microscope into a gold surface and then withdrawing the tip by a few nanometers. Past experiments on these nanowires have measured the distance between gold atoms in the nanowire to be significantly larger than the distance normally expected in gold, a finding that had been widely disputed. However the present theoretical study explains this anomalous distance by its estimation that gold atoms arrange in a zigzag fashion rather than in a straight line.
These theoretical simulations were run by Prashant Jain, a physical chemist from the Georgia Institute of Technology, Atlanta on a powerful IBM supercomputer housed at the Institute’s Center for Computational Molecular Science and Technology co-directed by Dr. C. David Sherrill. The simulation starts by imposing an initial guess arrangement of the gold atoms, and proceeds by allowing the atoms to take up the most favored placement, as governed by the laws of quantum physics. “A zigzag arrangement is more favored in a metal nanowire, since the metal atoms prefer to have four neighbors rather than just two as in a straight line arrangement,” the study says.
Another general point raised by this research is that there can be more than one highly favorable outcomes of a given situation and the simulation ends up in a particular outcome depending on how close it is to the initial guess. Thus by careful choice of the starting guess, not only can a computer simulation predict the results of a real experimental situation at hand, but also identify realms not explorable by present-day experiments.
This research is poised to appear in the journal Structural Chemistry.