First-Principles Prediction of Small Molecule Adsorption in MOF-74 Variants

Using density functional theory (DFT), we predict binding energies of flue gas molecules (CO, CO$_{2}$, H$_{2}$O, H$_{2}$S, N$_{2}$, NH$_{3}$, SO$_{2}$, and H$_{2})$ and small hydrocarbons (CH$_{4}$, C$_{2}$H$_{2}$, C$_{2}$H$_{4}$, C$_{2}$H$_{6}$, C$_{3}$H$_{6}$, and C$_{3}$H$_{8})$ in a variety of ``MOF-74'' variants.~ Using a harmonic approximation to compute quantum zero-point and thermal corrections, we compute binding enthalpies for comparison with experimental heats of adsorption.~ Our study is performed using vdW-DF2, a fully nonlocal dispersion-corrected density functional along with Hubbard U corrections on 3$d$-orbital electrons as appropriate.~ We study MOF-74 variants, ``M-MOF-74'', where ``M'' is chosen to be any divalent third-row metal cation (M$=$ Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn).~ Additionally, we study ``M-MOF-74'' systems with ``meta-dobdc'' as the linker (as compared to the traditional ``para-dobdc'').~ We compare with experiment when available and find reasonable agreement. ~We identify trends, and compare with experiment where available, finding excellent agreement. This work supported by DOE through the EFRC on Gas Separations for Clean Energy Technologies; computational resources provided by NERSC.~