Dataset for: Understanding methane cleavage on medium-entropy oxides

This dataset accompanies the article "Understanding methane cleavage on medium-entropy oxides" by S. Yuan, H. Song, Z. Wu and D. Jiang. It provides site-resolved, DFT-computed adsorption energies and climbing-image nudged-elastic-band (CI-NEB) activation barriers for the first C-H bond cleavage of methane (CH4 -> CH3 + H) on the (100) surface of a medium-entropy oxide, the equimolar quaternary oxide Mg0.25Zn0.25Ni0.25Cu0.25O. CONTENTS (two data files + documentation) methane_activation_MEO_dataset.csv - 77 elementary C-H cleavage reactions (30 heterolytic, 21 homolytic-trans, 26 homolytic-cis), tabulated in 12 columns: a reaction identifier, the mechanism, the site indices and identities of the CH4-, CH3- and H-hosting sites, the three adsorption-energy descriptors (adsorption energy of CH4, CH3 and H), and the CI-NEB activation energy Ea. site_adsorption_energies.csv - adsorption energies of H, CH3 and CH4 at each of the 16 lattice sites of the MEO (100) cell (8 metal-cation sites and 8 lattice-oxygen sites, indexed 1-16). These site indices are the same indices used in the reaction identifiers, so the two tables can be joined on the site index. SITE-NAMING SCHEME Each reaction is identified by a three-number code i_j_k: i is the cation site on which CH4 is adsorbed, j is the site that hosts the CH3 fragment after cleavage, and k is the lattice-oxygen site that hosts the abstracted H atom. For heterolytic cleavage the CH3 group remains on the original cation (j = i); for the homolytic pathways j and k are both lattice-oxygen sites, and "trans"/"cis" denote their relative geometry around the cation. SIGN CONVENTION All energies are in eV. Adsorption energies follow E_ads(X) = E(X/slab) - E(X,gas) - E(slab), so a more negative value indicates stronger binding. Activation energies are positive. COMPUTATIONAL DETAILS All calculations were performed with VASP 6 using the PBE functional, PAW pseudopotentials (Ni_pv for Ni), a 450 eV plane-wave cutoff, a 3x3x1 Gamma-centred k-mesh, and force and energy convergence thresholds of 0.05 eV/A and 1e-5 eV. A Hubbard correction (DFT+U, Dudarev) of U-J = 6.2 eV was applied to the Ni 3d states, together with Grimme DFT-D3 dispersion and spin polarisation. The surface was modelled as a five-layer 4x4 Mg0.25Zn0.25Ni0.25Cu0.25O (100) slab with at least 15 A of vacuum; the top two layers were relaxed while the bottom three were fixed at the bulk geometry. The cation sublattice was generated by random redistribution of the equimolar Mg/Zn/Ni/Cu cations over 200 independent realisations, and the configuration with one of the lowest surface energies was retained as the representative model. Transition states were located with the climbing-image nudged-elastic-band method using five intermediate images.