The origins and later developments of molecular orbital theory

Abstract

Hund in 1926 speculated on the assignment of quantum numbers for the electronic states of diatomic molecules, basing his assignments on the correlation between the diatomic states and those of the united atom limit. Mulliken, who had earlier considered the problem of this assignment using old quantum theory, followed Hund in 1927, in the new quantum theory, correlating the states of a diatomic molecule from the united to the separated atoms. In 1932, he introduced the term orbital for the one‐electron states of an atom or molecule. He was the first to seriously explore the orbitals of polyatomic molecules (1932). Burrau in 1927 made the first successful attempt to solve the Schrodinger's equation for H 2+, and Condon (1927) assigned two electrons to Burrau's orbital to obtain an estimate of the binding energy of H2. Lennard‐Jones (LJ) (1929) introduced the linear combination of atomic orbital model, and following the aufbau principle showed that this explained the paramagnetism of O2. Slater (1929) wrote many‐electron wave functions as determinants of spin‐orbitals, and LJ (1949) showed that with this formulation molecular orbitals (MOs) could be transformed into bond‐localized functions; this provided the link to the valence bond approach and the traditional view of the chemical bond. Huckel (1930) was the first to develop a semiempirical MO model for π‐electron hydrocarbons, and this was later extended by others for all‐electron wave functions. Boys (1950) saw the implication of Gaussian functions for calculating the electron repulsion integrals needed for ab initio calculations, and a later approach by Kohn and coworkers (1964 and 1965) produced a density functional MO theory in which electron repulsion is calculated from the whole electron density. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Chemical Bonding: The Journey from Miniature Hooks to Density Functional Theory

“…At the same time as the Heitler-London approach was proving scientifically and intuitively successful, an alternative quantum mechanical approach, molecular orbital theory, was being developed [279][280][281]. This approach was pioneered by Robert S. Mulliken [282][283][284][285][286][287][288][289], John Lennard-Jones [290][291][292], and Friedrich Hund [293,294] and ultimately described the bonding not in terms of localized bonds between two atoms but multi-center bonds over many atoms.…”

Momentum-selective orbital hybridisation

“…In molecular orbital (MO) theory 1 , the linear combination of atomic orbitals is the decisive element of chemical bonding 2 , while in the valence bond (VB) picture, it is the overlap between hybridised atomic valence orbitals 3 . In both models, if two atoms form a bond, the bonding strength is determined by the orbital overlap in the interaction potential 4 , 5 .…”

A Critical Look at Linus Pauling’s Influence on the Understanding of Chemical Bonding

“…However, it is fair to say that problems like the homolytic bond breaking of electron-pair bonds are more easily dealt with using VB calculations, which remains an important approach in the toolbox of quantum chemical methods [ 99 , 100 , 101 , 102 , 103 , 104 , 126 , 127 ]. The VB and MO methods have been compared and discussed in several papers, which shed further light on the two approaches [ 128 , 129 , 130 , 131 , 132 , 133 , 134 ].…”