Monday, January 17, 2011

What has quantum chemistry really achieved?

A small part only of the body of contributions of quantum mechanics to chemistry has been purely quantum-mechanical in character; only in a few cases, for example, have results of direct chemical interest been obtained by the accurate solution of the Schrodinger wave equation... The principal contribution of quantum mechanics to chemistry has been the suggestion of new ideas, such as the resonance of molecules among several electronic structures with an accompanying increase in stability.
Linus Pauling, Preface to The Nature of the Chemical Bond, First edition 1938

I wonder if this is still true today. Most computational chemists would bridle at that suggestion. But, I suspect that Pauling's point could still be argued today. Quantum mechanics has introduced important qualitative concepts such as potential energy surfaces, transition states, conical intersections, hybrid orbitals, ligand field theory, frontier orbitals, selection rules, .... These concepts are of far greater significance and success than the results of any detailed computations. Indeed the latter are largely of use to validate (and learn the boundaries of validity) of these concepts.
I welcome the views of readers.

1 comment:

  1. No that's an interesting topic! Modern chemical research would probably be lost without numerical quantum chemistry (at least large parts of it). Even in the fields where one would assume that the qualitative concepts are more important (e.g. organic synthesis) rely heavily on quantum chemistry nowadays (more and more position are established in computational organic chemistry).
    The question, which makes me wonder is: what else will quantum mechanics bring to chemistry? E.g. what’s the role of EPR like phenomena in (bio-)chemistry?
    So we can’t go behind numerical quantum chemistry but is it everything QM has to say about chemistry?
    Cheers & thanks for your cool blog