Isaiah Shavitt

The scientific achievements of Isaiah Shavitt are reviewed. These start with the Boys and Shavitt 1956 publications on the calculation of virial coefficients and the H₃ potential surface, two of the first applications of the newly available computer to chemistry. The list of landmark achievements also includes the Gaussian transform method for calculating multicenter integrals of Slater-type orbitals and the first proposal of contracted Gaussians as basis orbitals. Shortly before Shavitt left Israel in 1967, he began a long string of seminal contributions to the method of configuration interaction, including schemes for automatic generation of lists of configuration state functions and for selecting the configurations with the largest contributions to the total energy. With these methods, he carried out extensive (for the time) configuration interaction calculations using Slater orbitals and minimum basis sets. In subsequent years at Battelle and Ohio state University, with help of a notable group of postdoctoral fellows and graduate students, Shavitt produced, with ever increasing accuracy, many carefully done and detailed molecular studies, including C₆H₆, CH₂ and the H₂O vibrational surface. Even more influential were his contributions to developing new techniques, particularly obtaining eigenvalues of large matrices and developing the graphical unitary group approach to configuration interaction and related correlation energy methods. The ideas originated by Shavitt throughout his career influence deeply the way we do quantum chemistry to this day. In all his work, Shavitt was noted for the thorough and careful computational procedures he insisted upon before a paper was considered complete.