 Radial distribution function

In a homogeneous isotropic one-component fluid, $g(r)$ is the conditional number density at separation $r$ from a tagged particle divided by the bulk number density $n$. Thus the displayed shell contains the mean number of neighbours. For an uncorrelated ideal gas $g(r)=1$ away from the tagged particle; repulsive cores suppress small separations, while liquid coordination shells can produce damped oscillations approaching one at large distance. This is a pair correlation, not a normalized one-particle radial probability density. The static structure factor measures its Fourier-space counterpart.

The radial distribution function (RDF), also known as the pair distribution function (PDF), is a statistical measure used primarily in the fields of chemistry, physics, and materials science to describe how density varies as a function of distance from a reference particle within a system of particles. It provides insight into the structural properties of a material, particularly in liquids and gases but also in solids.