Isaiah Shavitt: Computational chemistry pioneer

Isaiah (Shi) Shavitt (1925-2012) was a pioneer in using digital computers to study chemical problems. From the days of vacuum tube computers with no floating point arithmetic to the days of massively powerful computers, he showed how we could solve otherwise intractable chemical problems by making use of computers. He started with a statistical mechanical problem and soon switched to quantum mechanical problems. He and his associates showed how the configuration interaction method worked, both in terms of advantages and difficulties. An early problem was the effect of tunneling on kinetics calculations on an H3 potential energy surface. Later problems included the p-electron excited states of benzene and the lowest excited state of methylene. He showed how spin-eigenfunctions could be used efficiently in configuration interaction calculations instead of Slater determinants. His leadership led to the Columbus suite of programs put together with many collaborators.