Researchers at the Swiss Federal Institute of Technology in Lausanne (EPFL) analyzed two massive databases that record the structural patterns of more than 80,000 known and predicted materials. They were surprised to discover that some 60 percent of materials had a unit cell in which the total number of atoms was a multiple of four.
The full findings of the study were published last week in the journal npj Computational Materials.
As scientists are prone to do, the team set out to look for an explanation for the unexpected pattern. At first, they thought it might be just a computing bug relating to how the material structures are classified and recorded in the databases.
In the end—while the team has managed to rule out several possible explanations—they have had to report that the mystery remains unsolved.
The team did make one promising finding, however, which may help future studies into the mysterious structural phenomenon. When the researchers applied a form of artificial intelligence (AI) to the problem, they found that it could predict if a compound will follow the Rule of Four with an 87 percent success rate.