## History

Building on the founding discoveries and theories in the history of quantum mechanics, the first theoretical calculations in chemistry were those of Walter Heitler and Fritz London in 1927. The books that were influential in the early development of computational quantum chemistry include Linus Pauling and E. Bright Wilson's 1935*Introduction to Quantum Mechanics – with Applications to Chemistry*, Eyring, Walter and Kimball's 1944

*Quantum Chemistry*, Heitler's 1945

*Elementary Wave Mechanics – with Applications to Quantum Chemistry*, and later Coulson's 1952 textbook

*Valence*, each of which served as primary references for chemists in the decades to follow.

With the development of efficient computer technology in the 1940s, the solutions of elaborate wave equations for complex atomic systems began to be a realizable objective. In the early 1950s, the first semi-empirical atomic orbital calculations were carried out. Theoretical chemists became extensive users of the early digital computers. A very detailed account of such use in the United Kingdom is given by Smith and Sutcliffe.

^{[1]}The first

*ab initio*Hartree–Fock calculations on diatomic molecules were carried out in 1956 at MIT, using a basis set of Slater orbitals. For diatomic molecules, a systematic study using a minimum basis set and the first calculation with a larger basis set were published by Ransil and Nesbet respectively in 1960.

^{[2]}The first polyatomic calculations using Gaussian orbitals were carried out in the late 1950s. The first configuration interaction calculations were carried out in Cambridge on the EDSAC computer in the 1950s using Gaussian orbitals by Boys and coworkers.

^{[3]}By 1971, when a bibliography of

*ab initio*calculations was published,

^{[4]}the largest molecules included were naphthalene and azulene.

^{[5]}

^{[6]}Abstracts of many earlier developments in

*ab initio*theory have been published by Schaefer.

^{[7]}

In 1964, Hückel method calculations (using a simple linear combination of atomic orbitals (LCAO) method for the determination of electron energies of molecular orbitals of π electrons in conjugated hydrocarbon systems) of molecules ranging in complexity from butadiene and benzene to ovalene, were generated on computers at Berkeley and Oxford.

^{[8]}These empirical methods were replaced in the 1960s by semi-empirical methods such as CNDO

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