Robert Mulliken

Robert Mulliken received the 1966 Nobel Prize in Chemistry for his fundamental theoretical work concerning chemical bonds and the electronic structure of molecules, primarily through his development of molecular orbital theory. The Nobel committee cited his work as having created a unifying theoretical framework for understanding molecular structure and spectra.

Mulliken's molecular orbital theory treats electrons in a molecule as delocalized over the entire molecule, occupying orbitals described by combining atomic orbitals into mathematical wavefunctions. In contrast, valence bond theory, championed by Linus Pauling, describes bonds as the overlap of localized atomic orbitals between pairs of atoms.

Mulliken spent the majority of his career at the University of Chicago, where he joined the faculty in 1928 and remained active for decades. He also spent time at the University of Florida in his later years, but his most influential work on molecular orbital theory was conducted at Chicago.

Mulliken population analysis is a method, introduced by Mulliken, for assigning electron density in a molecule to individual atoms by partitioning the overlap population between basis functions equally between the two atoms. Although it has known limitations and has been partly superseded by other charge-partitioning schemes, it remains a widely used tool in computational chemistry software.