2.5 Theoretical calculations
GCMC simulations were carried out using the Sorption program (BIOVIA Material studio 2019) to investigate the interactions between the framework and gas molecules. In our work, the crystal structures of MIL-120Al were chosen for our related simulations without further geometry optimization. A cut-off radius of 18.5 Å was used to handle the non-bonding interactions and the Ewald & Group summation method was applied to calculate the long-range electrostatic interactions. Each state point of the GCMC simulations contained 1 × 107steps to guarantee equilibration, followed by 1 × 107steps to sample the required thermodynamics properties. The MOF frameworks were treated as rigid structures by fixing the atoms at their crystallographic positions, which has been proven to yield accurate results in a large variety of GCMC studies. COMPASSII force field was adopted to describe the interactions for the atoms in our simulations. The partial charges for all atoms were derived using the DFT method (GGA-PBE/DNP).41