where 𝑖 and 𝑗 denote interacting atom pairs, i M refers to the multipole moments of atom i , interacting with atom j via multipole interaction tensor ij . In this work, the multipole expansion is truncated at quadrupole level, which are found to be sufficient for the description of the electrostatic interactions in water. To avoid singularity, we damp the charge-charge interaction using the Tang-Toennies damping function, )