What made possible the accurate calculations of NMR spin–spin coupling constants?

Abstract

The 1990s were an exciting time at the Quantum Theory Project of the University of Florida, during which several new developments in coupled cluster (CC) theory took place. One in particular is the development of the equation of motion coupled cluster (EOM-CC) method. It was realized that the EOM-CC excited states could be used to compute second-order properties in a sum over state formulation and the benchmark molecular polarizability calculations have since shown that EOM-CC performs remarkably well. The NMR spin–spin coupling is also a second-order property, and thus calculable by the new EOM-CC methodology. It was a common observation of reviews published at the time that a need existed for accurate nuclear magnetic resonance (NMR) indirect spin–spin coupling constants for medium-size molecules. This article is a first-hand account of the development of the EOM-CC methods for NMR spin–spin coupling constants and their successful applications to problems of interest.