Thirty years ago Pulay figured out an efficient method to determine a molecule's shape, thus paving the way for Nobel winners Pople's and Kohn's work. Kohn and Pople developed theoretical ways to study molecules and their interactions using computers. Pulay provided essential groundwork for their advances. To do so, Pulay looked at the relationship between a molecule's shape and its energy state.
Molecules tend to act like lazy people - they like to be at the lowest energy state.
The energy state determines the arrangement of atoms in a molecule. Pulay realized that since atomic forces can be directly calculated, the energy minimums, and therefore the shapes, could be determined. He created computer programs and software that made this easier to do. However, his methods made it easier to determine large molecular structures containing hundreds of atoms. Pretty soon theoretical work went from a stepchild of chemistry to an essential function that is applied hand in hand with experimentation.