Nuclear Motion Is Classical: Spectrum of a Magic Protonated Water Cluster

The assumption that nuclear motion is classical explains many phenomena. The problems of Schrödinger’s cat and the EPR paradoxon do not exist in a perfectly deterministic theory. All it needs is to describe nuclear motion classically right from the beginning. To establish this simple idea, it must be tested for as many examples as possible. In the present paper, we use ab initio molecular dynamics to investigate the infrared spectrum of a ‘magic’ protonated water cluster H 3 O + (H 2 O) 20 which exhibits some features that were believed to afford a quantum treatment of nuclear motion. The role of the temperature in contrast to a quantum mechanical description is discussed.