Thirdly, we consider multiple atoms with chemical bonds. Figure (a) shows a schematic illustration of multiple atoms. Multiple atoms often involve not only electric interactions but also Lennard-Jones, bond, angle, and dihedral angle interactions. To treat such multiple atoms, we firstly expanded atoms 1, 2, . . . , N into densities ρ 1 , ρ 2 , . . . , ρ N . Then, we calculated the movement of these N atoms by the generalized form of the equation ( ) and