Nonbonding parameters of AMBER force field have been refined based on ab initio binding energies of CO2–[C7H5N2]？ complexes. The energy and geometry scaling factors are obtained to be 1.2 and 0.9 for and parameters, respectively. Molecular dynamics simulations of CO2 molecules in rigid framework ZIF-11, have then been performed using original AMBER parameters (SIM I) and refined parameters (SIM II), respectively. The site-site radial distribution functions and the molecular distribution plots simulations indicate that all hydrogen atoms are favored binding site of CO2 molecules. One slight but notable difference is that CO2 molecules are mostly located around and closer to hydrogen atom of imidazolate ring in SIM II than those found in SIM I. The Zn-Zn and Zn-N RDFs in free flexible framework simulation (SIM III) show validity of adapting AMBER bonding parameters. Due to the limitations of computing resources and times in this study, the results of flexible framework simulation using refined nonbonding AMBER parameters (SIM IV) are not much different from those obtained in SIM II. 1. Introduction The increase in carbon dioxide (CO2) in Earth’s atmosphere is a subject of worldwide attention as being the cause of global warming. Human activities such as combustion of fossil fuels (coal, oil, and natural gas) in power plants, automobiles, and industrial facilities are main sources of CO2 emission. The cost-effective and scalable technologies to capture and store CO2 are now of great interest [1–7]. The low energy requirement technologies based on adsorption processes are highlighted as promising methods, stimulating recent works to investigate suitable adsorbent materials. Metal-organic frameworks (MOFs) are a class of nanoporous materials that are promising candidates for CO2 capture, due to their potential applications in separation processes, catalysis, and gas storage [8–14]. Zeolitic imidazolate frameworks (ZIFs) are subclass of MOFs, in which positive metal ions such as Zn, Co, and Cu are linked by ditopic imidazolate ligands [15, 16]. Some ZIFs are attracted as materials which are used to keep the emissions of CO2 out of the atmosphere in hot energy-producing environments like power plants due to their exceptional chemical and thermal stabilities and nontoxic crystals [17–19]. The ZIF-11 is one of ZIFs which exhibits the RHO topology. It is composed of Zn2+ ion clusters linked by dipotic benzimidazolate ([C7H5N2]？) ligands with chemical formula Zn[C7H5N2]2 [15] (see Figure 1). Figure 1: The topologies of ZIF-11, [C 7H 5N 2] ？, and CO 2. The
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