"The Mystery of the 'Rule of Four' in Materials Science"

Scientists have observed an unexpected pattern, dubbed the "Rule of Four," in two major electronic structures databases, where around 60% of structures have primitive unit cells made of a multiple of four atoms. Despite extensive investigation, including machine learning algorithms, researchers have been unable to explain this phenomenon, ruling out factors such as software errors, chemical properties, and formation energies. While the lack of a compelling explanation is a rare example of a scientific paper describing a negative result, the team's prediction algorithm achieved an 87% accuracy in determining whether a compound follows the Rule of Four, hinting at the potential role of undiscovered small chemical groups in cells.