Advancing solid-state band gap predictions

Abstract

Perhaps the most important property of a material is its fundamental band gap. This is the energy difference between adding and subtracting one electron from a system. It distinguishes metals from insulators and gives us information about the electronic response of the material to external influences. This is crucial in myriad technological applications like batteries, semiconductors, alloys, electronic devices, and photovoltaic materials, to name a few. Band gap predictions employing quantum simulations have steadily progressed over the years, but an accurate method valid across the broad spectrum of materials with diverse band gaps was lacking. Wing et al. (1) take a decisive step forward in the first-principles prediction of fundamental band gaps with accuracy rivaling experimental error bars in their measurement, a feat that builds upon the contributions of multiple research groups during the last few decades. For many years, the workhorse of computational materials modeling has been density functional theory (DFT), particularly for properties like band gaps where quantum effects are preponderant. DFT is a relatively simple model whose roots precede the formulation of quantum mechanics (2). It essentially describes electrons as independent particles interacting via an effective potential obtainable from an exchange-correlation energy functional of the electron density. Somewhat paradoxically, the existence of this functional can be easily proven, but its practical realization has turned out to be much more challenging than perhaps originally envisioned. For several decades, researchers have systematically improved the accuracy of DFT, making it a valuable aid for chemistry, physics, and materials science. However, across the broad range of solid-state materials, the fundamental band gap has remained stubbornly difficult to predict with high accuracy. The form of DFT most appropriate to calculate band gaps is known as generalized Kohn–Sham theory (3), a model where the functional depends on all the orbitals that electrons can … [↵][1]1Email: guscus{at}rice.edu. [1]: #xref-corresp-1-1