Pair distribution function

The pair distribution function describes the distribution of distances between pairs of particles contained within a given volume. Mathematically, if a and b are two particles, the pair distribution function of b with respect to a, denoted by ${\displaystyle g_{ab}({\vec {r}})}$ is the probability of finding the particle b at distance ${\displaystyle {\vec {r}}}$ from a, with a taken as the origin of coordinates.