In order to accurately understand the interfacial properties of nanoparticles, one must first be able to describe where the interface of interest is located in space. Once the interface is identified then not only can the interfacial properties be measured but also the inter-nal distribution of the components within a nanoparticle can be measured, which provides significant insight into the structure of the nanoparticle. Spherical Density. For nanoparticles that are approximately spherical, the interface of the nanoparticle can be described by identifying the radius of the nanoparticle from the particle's center of mass. Then the density of their various components and its environments can be calculated with reference to the aggregate's center of mass ('spherical density'). There are numerous MD studies that measure the density of components of polymer micelles using this approach, but there are limited open-sourced codes that can be used to carry out such analysis. The PySoftK spherical\_density tool allows users to easily calculate the spherical density over time, even for structures with varying molecule numbers throughout the simulation. It computes the average density (over time) with respect to the distance from the center of mass of the molecular structure. This is achieved by dividing up the simulation space into spherical bins with reference to the origin at the center of mass of the aggregate. For each of these bins, the number of particles in them is counted and divided by the volume of the bin. This calculation is described in Equation .