Hitting a solid makes a sound, because the pattern of molecular vibrations unique to a solid is a sound wave.A sound wave is a spatially spread wave that follows a law called the "Debye law" (the number of sound waves is proportional to the square of the frequency).However, it has long been suggested that glass has a vibration pattern that cannot be explained by the Debye law, but it was unclear what it was and what law it followed.

　In this research, we performed a large-scale computer simulation and succeeded in elucidating the vibration pattern peculiar to glass.Specifically, the vibration patterns of molecules in glass were investigated in detail by performing molecular simulations dealing with each molecule.

　As a result, it was discovered that in addition to sound waves, glass has spatially localized vibrations that are completely different from sound waves.It was found that the vibration pattern is a spatially localized vibration, that is, a vibration pattern in which some molecules in the space vibrate greatly while other molecules hardly vibrate.

　Furthermore, it turns out that this localized oscillation follows a completely new law that is different from the Debye law.That is, it was established that the sound wave according to the Debye law and the localized vibration according to another law are mixed in the glass.

　This result conclusively shows that glass is essentially different from ordinary solids.This achievement is said to put an end to the long-controversial problem of the vibration characteristics of glass.Furthermore, it is expected that the basic understanding of the thermal and mechanical properties of glass will be greatly advanced, leading to the technology for developing new glass materials.

Paper information:[Proceedings of the National Academy of Sciences of the United States of America] Continuum limit of the vibrational properties of amorphous solids