Molecular Scientists and Molecular Science: Some Reminiscences. In it he made a commonly quoted statement highlighted below. I reproduce it in context.
....I would have liked first to say something about Molecular Quantum Mechanics (MQM) problems. .... The general idea [of Lowdin's conferences] was that with old-fashioned chemical concepts, which at first seemed to have their counterparts in MQM, the more accurate the calculations became the more the concepts tended to vanish into thin air. So we have to ask, should we try to keep these concepts-do they still have a place-or should they be relegated to chemical history. Among such concepts are electronegativity....., hybridization, population analysis, charges on atoms, even the idea of orbitals, ....Roald Hoffmann has argued these concepts do have a role. I would certainly agree. Computations should support, elucidate, and clarify concepts, not eliminate them. The issues are nicely discussed in 5 papers every computational chemistry student should read.
I thank Anna Painelli for bringing this quote to my attention.