The graph below is a plot of RDF from Gromacs MD. It was reported that the coordination number of one substance round another (for here CO2 round anion) can be obtained from the relation:

CN = 4 x 3.142 x density x (integral r2g(r)dr)

The limit of integration is within the region of the first peak.

We integrate the first peak using the origin but we are not sure to proceed to the next stage because in the formula "r" is squared but in the graph, it is not.

Can anybody shed more light on how to proceed and eventually obtain the solubility of the CO2? The system is an ionic liquid and CO2.