Eccentricity. Eccentricity, a metric quantifying a structure's deviation from a perfect sphere, serves as a useful tool for assessing the shape of spherical-like soft matter aggregates. The ecc tool calculates the eccentricity for any molecular structure by leveraging the MDAnalysis function moment_of_inertia() and employing the following formula: where ϵ is the eccentricity value, I min is the minimum moment of inertia across all axis of the molecule(s), and I mean is the mean moment of inertia over all axis of the molecule(s). A perfect sphere corresponds to ϵ = 0, while increasing values indicate more oblong structures.