First-Principles Calculations of the Role of Dispersive Interactions in CO$_2$ binding in metal-organic frameworks

Metal-organic frameworks (MOFs) have attracted much attention over the past 20 years for their possible applications in gas storage. In this study, we provide computational insight into what makes a MOF structure optimum for CO$_2$ capture. We present a density functional theory-based study of the electronic and structural properties of recently synthesized frameworks M'$_3$[(M$_4$Cl)$_3$(BTT)$_8$]$_2$, with M'=extraframework cation and M=Ca [1]. We study the interactions between CO$_2$ and different binding sites, and predict an unexpected favored binding site at the organic linker. We explore how binding energies are affected by the ordering and type of the extraframework cations. Finally, we address the role of dispersion forces by employing a recent non-local van der Waals functional [2], and compare with a DFT+D approach [3].\\[4pt] [1] M. Dinca et al., {\sl J. Am. Chem. Soc.} 128, 16876 (2006)\\[0pt] [2] M. Dion et al., {\sl Phys. Rev. Lett.} 92, 246401 (2004)\\[0pt] [3] A. Tkatchenko et al., {\sl Phys. Rev Lett.} 102, 073005 (2009)