A pair potential specifies an interaction energy for each pair of particles, with total energy given by the sum over distinct pairs. For a radial difference-only potential
in 
, the energy is
 |
Stability means that 
for some constant 
, for every finite
particle configuration. This linear lower bound prevents
the energy per particle from diverging to minus infinity as particles accumulate.
An integrable tail satisfies 
for some 
.
