= London dispersion force
{c}
{title2=$U(r)=-C_6/r^6$}
{wiki}
Named after <Fritz London>, this is an attractive interaction between fluctuating <electric dipoles> of atoms or molecules, present even without a permanent dipole. At large separation compared with atomic size in the nonretarded regime, the dipole interaction scales as $r^{-3}$ and its second-order ground-state energy correction is negative and scales as $r^{-6}$. Differentiating the energy gives an attractive <force> of magnitude $6C_6/r^7$. The short-distance overlap regime and the very-long-distance retarded regime require different descriptions.
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