candidate: The famous Bohr model of the hydrogen atom is a simple example , but the EBK method also gives accurate predictions for more complicated systems , such as the dinuclear cations H2 + and HeH2 + . < / ref > In 1918 , Einstein developed a general theory of the process by which atoms emit and absorb electromagnetic radiation ( his " A " and " B " coefficients ) , which is the basis of lasers ( stimulated emission ) and shaped the development of modern quantum electrodynamics , the best - validated physical theory at present .