Scientific American: Most of my day job involves simulating the behavior of molecules like drugs and proteins using computer models. The field is more an art than a science, partially because the systems that are being modeled are too complex and ill-understood to succumb to exact solutions. Success often depends on experience and intuition gained by working on similar systems. That does not mean there are no correct predictions, but it does mean that surprises are more common than we think and that many phenomena are...