The anthropogenic emission of greenhouse gases, mainly CO₂, is considered to be one of the most challenging environmental threats related to global climatic change. Herein, for the first time, we accurately interpreted the interaction of guest molecules such as H₂O, CO₂ and N₂, the main constituent of flue gas, to a coordinatively unsaturated (CUS) square pillared fluorinated metal organic framework (MOF) using a grand canonical Monte Carlo (GCMC) simulation with the help of a specific forcefield. This specific forcefield is derived from the interaction energy profile of the guest molecules to the framework attained from the periodic-density functional theory (DFT) calculations. The DFT-derived forcefield effectively safeguarded the ability of the coordinatively unsaturated square pillared fluorinated MOF for CO₂ separation in the presence of moisture.