where E gp is the energy of a single molecule optimised in the gas phase. While in the following the underlying embedded energy is calculated according to different schemes, cohesive energies are always computed according to Equation ( ). At the one-body level the embedded energy is simply the sum of QM energy of the "central molecule" in the field of the surrounding point charges, and the interaction energy calculated between the "central molecule" and all other cluster molecules through the LJ pair potentials. It is denoted as AC(1)-QM/MM in the following and simply provided by the energy term