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Quantum mechanics has provided chemistry with two general theories, valence bond (VB) theory and molecular orbital (MO) theory. The two theories were developed at about the same time, but quickly diverged into rival schools that have competed, sometimes fervently, on charting the mental map and epistemology of chemistry. Three practitioners of MO and VB theory talk - fighting a little, trying to understand - of the past and present of these two approaches to describing bonding in molecules.
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Hoffmann et al. (2003) studied this question.
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