First Principles Investigation of Adsorption Mechanisms and Charge Redistribution for CH4/Ni(111) Surface

Abstract

Liquefied natural gas (LNG) is predominantly methane (CH₄), and the characterization of its interaction to metallic materials (e.g., nickel) is important for evaluating structural stability during cryogenic storage and transport. Using density functional theory within the GGA–PBE framework as implemented in QuantumATK 2023, the adsorption behavior of a single CH₄ molecule on a six-layer Ni(111) surface was evaluated in this work. The surface was simulated using a 4×4 slab configuration with a vacuum layer sufficiently large to prevent interactions between periodic images. The upper three Ni layers and methane molecule were completely relaxed during the optimization. The optimized structure shows that methane maintains its ideal tetrahedral geometry (C–H ≈ 1.11 Å) but the equilibrium C–Ni separation is approximately 3.21 Å, while Ni–Ni interlayer distances do not change significantly, indicating a minimal structural distortion of the metallic slab. The calculated adsorption energy (E_ads = −1.22 eV) indicates energetically favorable adsorption of methane on the Ni(111) surface, suggesting a relatively weak interaction characteristic of physisorption. Density of states (DOS) analysis further confirms that the electronic states near the Fermi level are dominated by Ni 3d orbitals, while methane-related states contribute only weakly, indicating negligible orbital hybridization and confirming the physisorption nature of CH₄ adsorption on the Ni(111) surface. Bader charge analysis further reveals negligible net charge transfer and minimal interfacial polarization. Electron density difference (EED) analysis reveals only minor charge redistribution at the CH₄/Ni(111) interface, indicating negligible charge transfer and supporting the weak physisorption nature of methane adsorption on the Ni(111) surface. In general, we find that the methane interaction with Ni(111), governed primarily by weak van der Waals forces, is relatively weak and no covalent bond or activation occurs. These results confirm the electronic and chemical inertness of methane on clean nickel surfaces under cryogenic conditions relevant to LNG storage and transport systems.