The number of theoretical studies of guests in fully flexible DUT-8(Ni) is, to our knowledge, limited to our previous works, probably due to the challenges of correctly modelling the Nickel nodes. However, given the available experimental adsorption data of CH x Cl 4-x molecules, it is a suitable benchmark system to test the adsorption properties without loss of generality. Experimentally different conditions for the adsorption of methane have been reported: Opening of the structure is observed at 111 K and 1 bar methane pressure, 30 but at 195 K and up to 2 bar no transition occurs. All chlorinated methanes are able to switch the framework from the cp to the op phase. An important factor for the capability to switch the MOF from cp to op, besides the energy gain, is the kinetic diameter of the guest (see Figure ). The kinetic diameter is also connected to the maximum loading, which in turn affects the total adsorption energy gain. Large diameters kinetically hinder the guest in entering the cp phase. Since we are mainly concerned with energetic arguments in this work, we will refrain from reproducing the kinetic arguments already made.