Scientists at the U.S. Naval Research Laboratory (NRL), in collaboration with Florida State University, have developed a method to simulate electron localization in real materials including imperfections and electron-electron interactions.
Electron localization is the tendency of electrons to become confined or clustered in small regions of a material much like humans have a tendency to cluster in cities across the country. Clustering can be caused by local factors such as material imperfections, or as in the case of the Earth, the presence of natural resources, river deltas, or other attractive geographic features.
Another cause for bunching is electron-electron interactions of repulsive Coulomb forces, the strong electrostatic force experienced by charged particles. There is a similar phenomenon among diverse human populations, when aversion or doubt that exists between communities exceeds the mutual benefit of working together and exchanging resources. Just as human migration affects society, electron localization affects material properties such as optical absorption and electron conductivity.
In classical mechanics, the locations of humans, cars, etc., can be tracked, at least in principle. Such tracking is not possible in quantum mechanics, where particle locations are instead given in terms of probability densities. The decay of the electron probability density inside a solid is a measure of electron localization.
In metals, the electronic states are delocalized, allowing electrons to move from site to site across the material. Imperfections and electron-electron interactions, however, can localize the electronic states, turning a metal into an insulator.
The majority of this work focuses on localization induced by either imperfections or electron-electron interactions. The authors present a new method overcoming roadblocks by combining first-principles density functional theory, the Anderson-Hubbard model, and the typical medium dynamical cluster approximation within dynamical mean-field theory.
The new method to simulate electron localization in real materials has been applied to monolayer hexagonal boron nitride, a large-gap insulator, and predicts that this is one material that requires both imperfections and electron-electron interactions to undergo an insulator-to-metal transition.