Molecular multipoles and (hyper)polarizabilities from the Buckingham expansion: revisited

Houxian Chen,Menglin Liu,Tianying Yan

Figure 1. A schematic Buckingham expansion, in which E can be external electric fields and field gradients, ρ(r) represents the polarizable charge distribution, and M(r) denotes permanent and induced multipoles. The equation corresponds to the Buckingham expansion in the traceless form, which is derived in equation (27).