One of the legends of science is that the 1933 Nobel Laureate Paul Dirac, after completing his formalism of quantum mechanics, paraphrased Shakespeare by commenting: “The rest is chemistry…”. This places a heavy burden on the shoulders of “chemistry” because “the rest” amounts to the quantitative description of the world around us and the prediction of all every-day phenomena ranging from the chemical reactions of atoms and small molecules via functional materials and medical drugs up to the integrated description of living organisms.

With the advent of electronic computers and with the subsequent exponential growth in computer power, it seemed to many that it was only a matter of time until the laws of quantum mechanics could be directly solved to predict the properties of macroscopic materials and, eventually, living organisms. However, even in the unlikely event that the available computing power would continue its exponential growth for decades to come, it would still take centuries before we could carry out Dirac’s program for relevant model systems of a catalytic process or an antenna molecule featuring in solar cells, let alone a living organism. We cannot wait that long and, fortunately, we need not. A hierarchical “multiscale” approach offers a realistic route to model complex, macroscopic systems, using as input only our knowledge of the laws of quantum mechanics, classical mechanics and statistical mechanics. Together with our expertise in electronic-structure analysis and creating chemical and physical models that catch the essence of the factors determining structure and reactivity, this paves the road to the holy grail of the molecular sciences: arriving at a fundamental understanding that provides a basis for rational design of functional or smart molecules and materials that serve human health and a more sustainable economy.