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Volume 135, 2007
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Spiers Memorial Lecture
Quantum chemistry: The first seventy years

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Abstract

Present-day theoretical chemistry is rooted in Quantum Mechanics. The aim of the opening lecture is to trace the evolution of Quantum Chemistry from the Heitler–London paper of 1927 up to the end of the last century, emphasizing concepts rather than calculations. The importance of symmetry concepts became evident in the early years: one thinks of the necessary anti-symmetry of the wave function under electron permutations, the Pauli principle, the aufbau scheme, and the classification of spectroscopic states. But for chemists perhaps the key concept is embodied in the Hellmann–Feynman theorem, which provides a pictorial interpretation of chemical bonding in terms of classical electrostatic forces exerted on the nuclei by the electron distribution. Much of the lecture is concerned with various electron distribution functions—the electron density, the current density, the spin density, and other ‘property densities’—and with their use in interpreting both molecular structure and molecular properties. Other topics touched upon include Response theory and propagators; Chemical groups in molecules and the group function approach; Atoms in molecules and Bader's theory; Electron correlation and the ‘pair function’. Finally, some long-standing controversies, in particular the EPR paradox, are re-examined in the context of molecular dissociation. By admitting the concept of symmetry breaking, along with the use of the von Neumann–Dirac statistical ensemble, orthodox quantum mechanics can lead to a convincing picture of the dissociation mechanism.

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Publication details

The article was received on 25 Oct 2006, accepted on 25 Oct 2006 and first published on 12 Dec 2006


Article type: Paper
DOI: 10.1039/B615518A
Citation: Faraday Discuss., 2007,135, 13-30
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    Spiers Memorial Lecture

    R. McWeeny, Faraday Discuss., 2007, 135, 13
    DOI: 10.1039/B615518A

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