To gain insight into the different contributions to the material's polarization response, we examine below a continuum model of the polarization of isolated nanoparticles. Quantum data used for the development of the model was generated as follows. Relaxed nanoparticle geometries were obtained using density functional theory by annealing in SIESTA, using a PBE /DZP approach and Troullier-Martins pseudopotentials obtained from the SIESTA Database. Polarizabilities α ii along Cartesian directions i were then calculated by applying an electric field E i of 0.0001 a.u. (0.005 eV/ Å in SIESTA units), and calculating the change in dipole moments µ i relative to the zero-field states: