where 𝐸 > (𝐑 > ) is the adiabatic potential energy of X at geometry 𝐑 > , 𝐸 ? (𝐑 ? ) is the adiabatic potential energy of Y at geometry 𝐑 ? , and 𝐸 @2 (𝐑 = ) is the interaction potential energy, which will be called the added-dimensions (AD) potential energy because that is a more suitable name for the general case introduced in Section 3.2. Therefore, at the dissociation limit where X and Y are separated, the added-dimensions potential energy 𝐸 @2 (𝐑 = ) is equal to 0. Let nX and nY be the number of atoms in X and Y. Since the potential energy depends only on internal coordinates, 𝐸 > (𝐑 > ) + 𝐸 ? (𝐑 ? ) has a lower dimensionality than 𝐸 = (𝐑 = ), and we label this sum as the lowdimensional (LD) adiabatic potential energy 𝐸 A2 (𝐑 = ). For example, if X and Y are both polyatomic, then