The Physics of Metal Clusters

Scientists often set the stage for their most productive advances by first developing simple models, even when sophisticated first‐principles tools are available. These models usually originate from the necessity to explain experimental observations. If the models are robust, then a variety of data fall into place, and successful predictions are made. If a model is “correct,” it is eventually found to be consistent with or derivable from fundamental theory. The Bohr model for atoms is a prime example. Ernest Rutherford's experiments showed that J. J. Thomson's “plum pudding” model of an atom, consisting of a positive spherical “pudding” embedded with negative electron “plums,” had to be replaced by Rutherford's nuclear picture, and subsequent optical data led to the Bohr model. Eventually quantum theory confirmed that the Bohr model is an excellent rudimentary representation for an atom. Although it has been superseded by more elaborate quantum theoretical approaches, this model is still taught to students of atomic physics because of the physical insight one gains by using the Bohr picture of an atom.