  We have computed the widely neglected first-order interaction between neutral
atoms. At interatomic separations typical of condensed media, it is nearly
equal to the 1/r^6 second-order London energy inferred from interactions in
gasses. Our results, without the exchange forces that lead to covalent bonding,
suggest that the quality of non-bonding attraction between neutral atoms of
molecules in condensed media differs from the 1/r^6 form usually ascribed to
it. If we add first-order and all second-order terms, we obtain energies nearly
five times the 1/r^6 London energies which dominate only at the atomic
separations found in gasses. For computation, we propose a practical, accurate
form of energy to replace the qualitatively inaccurate Lennard-Jones and
harmonic forms casually assumed to hold at the interatomic separations found in
condensed media.
