Isaiah Shavitt

The Gaussian Function in Calculations of Statistical Mechanics and Quantum Mechanics, chapter in Methods in Computational Physics (B. Alder, S. Fernbach, and M. Rotenberg, editors), Vol. 2, pages 1–45 (Academic Press, New York, 1963).
The Method of Configuration Interaction, chapter in Methods of Electgronic Structure Theory (Modern Theoretical Chemistry, Vol. 3) (H.F. Schaefer III, editor), pages 189–275 (Plenum Press, New York, 1977).

The Graphical Unitary Group Approach and Its Application to Direct Configuration Interaction Calculations, chapter in The Unitary Group for the Evaluation of Electronic Energy Matrix Elements (Lecture Notes in Chemistry 22) (J. Hinze, editor), pages 51–99 (Springer Verlag, Berlin, 1981).

Supercomputers and Chemistry (ACS Symposium Series 173), P.G. Lykos and I. Shavitt, editors (American Chemical Society), Washington, D.C., 1981), 278 pp.

The Unitary Group and the Electron Correlation Problem, chapter in New Horizons of Quantum Chemistry (P.-O Löwdin and B. Pullman, editors), pages 279–293 (Reidel, Dordrecht, 1983).

The Treatment of Electron Correlation: Where Do We Go from Here? chapter in Advanced Theories and Computational Approaches to the Electronic Structure of Molecules (C. E. Dykstra, editor), pages 185–196 (Reidel, Dordrecht, 1984).

Unitary Group Approach to Configuration Interaction Calculations of the Electronic Structure of Atoms and Molecules, chapter in Mathematical Frontiers in Computational Chemical Physics (D. G. Truhlar, editor), pages 300–349 (Springer-Verlag, Berlin, 1988).

The major contributions have been in the field of configuration interaction (CI) calculations of molecular electronic structure, including methodology and applications. The methodological studies included the introduction of configuration selection schemes for CI expansions and the Ak and Bk approximate CI methods, and the examination of the convergence behaviour of CI expansions and its dependence on the choice or orbitals and expansion terms. The most important methodological contribution has been the development of the graphical form of the unitary group approach and its adaptation for efficient multireference configuration interaction and related calculations. The resulting system of computer programs, widely distributed under the name COLUMBUS, is capable of calculations involving many millions of terms in the CI expansion. Other methodological contributions included the development of methods for the calculations of multicenter integrals for Slater-type orbitals and for the solution of very large matrix eigenvalue problems.

Applications included the calculation of potential energy surfaces, including H₃,H₂O, and CH₂, and the study of excited states of various molecules, including benzene and butadiene. Other studies compared different methods for the incorporation of electron correlation effects in electronic structure calculations, including perturbation-theoretical and coupled-cluster methods.