Pair Correlation Function Module
The pair correlation function gij(r) indicates the average number of atoms (of atomic species i) per unit volume of atomic species j atoms that are located at distance r from a target atomic species i atom. The number is expressed in terms of average density. The pair correlation function is calculated by preparing several time series data items, averaging those data times, and averaging those data items based on the number of atoms. The running integration number shows the number of atomic species j atoms that are located within a sphere of radius r from a target atomic species i atom as the center.