In 1929 Paul Dirac made a famous announcement:

Beginning almost immediately, physicists and chemists rose to Dirac’s challenge and developed the theoretical framework needed to calculate wavefunctions and energy eigenvalues for atoms, molecules, and solids.

By the mid 1960s, computers had sufficient speed and memory to solve the Schrödinger equation for atoms and small molecules by using the Hartree–Fock approximation. That variational method makes a simple guess at the many-electron wavefunction and ensures that each electron interacts with the external potential from fixed nuclei, with the classical electrostatic potential produced by the other electrons, and with a nonlocal exchange potential, which provides short-range repulsion between parallel electron spins. Many-body correlation effects—principally short-range repulsion between antiparallel spins—not captured by the Hartree–Fock approximation were studied by atomic physicists and quantum chemists using more sophisticated choices for the many-electron wavefunction. As a matter of taste, physicists studying correlation effects in solids preferred to...

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