Classical mechanics such as Force Fields (FFs) could be a shortcut. Force fields are employed for properties that don't need information about electronic structure and can be defined by the relevant conditions of temperature or pressure. In these cases, force fields offer a welcome reduction in cost. Existing force fields which have been routinely applied in MOF simulations are either the general force fields -such as UFF , TraPPE and DREIDING -or specific force fields designed for a particular group of MOFs , such as MOF-FF and QuickFF . Specific force fields are typically more accurate than general force fields, but are unsuitable for screening studies outside their parameterization. The general force field approaches are good at handling the chemical diversity of MOFs for reproducing experimental results such as crystal structures, bulk moduli, sublimation energies and fluid properties . However, they are not ideal for explaining structural transformation over external stimuli and for explaining donor-acceptor interactions in open metal site materials. Another problem is general force fields fail to model adsorption isotherms at the lower pressure region. Since the diverse inorganic fragments that comprise MOFs cannot be replicated by general force fields, a common approach is to reparametrize these force fields. The initial development of force fields for MOFs were force fields designed to accurately describe individual popular MOFs, such as extended MM3 for MOF-5, Cu paddlewheel-based MOFs and for the Flexible Metal-Organic Framework MIL-53(Al). Subsequently, force fields have been developed to accommodate a group of MOFs, BTW-FF for 6 popular MOFs associated with Cu, Zn, and Zr metal nodes; Becker at al 29 optimized a polarizable force field for CO2 and CH4 Adsorption in M-MOF-74 (M = Co, Cr, Cu, Fe, Mg, Mn, Ni, Ti, V, and Zn). QuickFF is a program that automates the derivation of force fields for MOFs. UFF4MOF took a different approach, aiming for universality rather than transferability and reached over 99% coverage of the 2014 CoRE database. Another approach frequently used is combining potentials from multiple generic force fields. Hamon et al. modelled adsorption of H2S into MIL MOFs by combining UFF for the inorganic part of the framework and the DREIDING inter-atomic potential for the organic part. The model matches the experimental adsorption isotherms quite well in the whole pressure range, confirming structural transitions occur in some pressure regions. Vandenbrande et al. reviewed five different force fields, three combined generic force-field (UFF/TraPPE, Drieding-UFF/TraPPE, MM3-MBIS) and two ab initio derived force fields (SAPTFF and MEDFF), for methane adsorption in Zr-based MOFs (UiO-66, UiO-67, DUT-52, NU-1000, and MOF808), found that UFF/TraPPE gives an acceptable agreement with the experiment in the UiO-66 framework for pressure between 30 and 80 bar. Meanwhile, other combined generic force fields do not accurately reproduce single molecule adsorption energies. The two ab-initio derived force fields gave a remarkable accuracy of the individual adsorption energies.