transformation between $\boldsymbol{\alpha}$-tensor in the Cartesian basis and $\mathbf{T}$-matrix in the spherical basis using the basis transformation between the exact Cartesian and the spherical multipoles (Eqn. \[eqn:multipole\]) and between the local fields and field gradients and the spherical multipoles (Eqn. \[eqn:field\]). In general, characterization of meta-atoms using $\boldsymbol{\alpha}$-tensor has been limited to dipolar regime, but recent advances in nanophotonics and metamaterials utilize higher-order multipole transitions coming from coupled plasmonic and high-index dielectric nanoantennas. These scattering systems with higher-order multipole transitions can be interpreted at a fundamental level using higher-order $\boldsymbol{\alpha}$-tensor, which can be easily obtained from $\mathbf{T}$-matrix using the facile basis transformation. Incorporated with the MST, the multipole approach can be a versatile theoretical framework in nanophotonics to rigorously investigate optical phenomena arising in coherently coupled multi-body systems [@Mishchenko2008]. Here, the well-defined symmetries and conservation laws can be treated at the microscopic level (single scattering object) using $\boldsymbol{\alpha}$-tensors, and the electromagnetic interaction between them are treated using the Green’s tensors. It is worthwhile to note that the potential applicability of $\boldsymbol{\alpha}$-tensor (or $\mathbf{T}$-matrix) into the MST has been mentioned in many previous papers, but only spherical particles have been generally considered. By simply taking nonspherical structured meta-atoms into account, the 