Assessing the Predictive Power of Density Functional Theory in Finite-Temperature Hydrogen Adsorption/Desorption Thermodynamics

Abstract

Density functional theory (DFT) has been widely employed to study the gas adsorption properties of surfacebased or nanoscale structures. However, recent indications raise questions about the trustworthiness of some literature values, especially in terms of the DFT exchange−correlation (XC) functional. Using hydrogen adsorption on metalloporphyrinincorporated graphenes (MPIGs) as an example, we diagnosed the trustworthiness of DFT results, meaning the range of expected variations in the DFT prediction of experimentally measurable quantities, in characterizing the gas adsorption/ desorption thermodynamics. DFT results were compared in terms of XC functionals and vibrational effects that have been overlooked in the community. We decomposed free energy associated with gas adsorption into constituting components (binding energy, zero-point energy, and vibrational free energy) to systematically analyze the origin of deviations associated with the most commonly adopted DFT functionals in the field. We then quantify the deviations in the measurable quantities, such as operating temperature or pressure for hydrogen adsorption/desorption depending on the level of approximations. Using chemical potential change associated with gas adsorption as a descriptor, we identify the required calculational accuracy of DFT to predict the room-temperature hydrogen storage material.

Effects of van der Waals Dispersion Interactions in Density Functional Studies of Adsorption, Catalysis, and Tribology on Metals

“…Yoon et al studied the contribution of vibrational energies to free energies of H 2 on metalloporphyrin-incorporated graphene using LDA, GGA, and vdW functionals. 121 For weak adsorptions, the zero-point energy and vibrational free energy significantly depend on the choice of vdW functionals (see Figure 9). For the Zn case, the difference of vibrational free energy of adsorbed H 2 is ca.…”

Transition-metal decorated graphdiyne monolayer as an efficient sensor toward phosphide (PH3) and arsine (AsH3)

“…We justify the limitation of our approach by the fact that the binding energies in eqn ( 2) are the DFT values at 0 K. In principle, realistic adsorption energies at finite temperatures require the exhaustive inclusion of the molecular vibrational free energy of the gas adsorbates. 49 This contribution is generally ignored, and it is speculated that the immense chemical bonds (i.e., strong binding energies) of gas/ sensor interfaces yield negligible molecular vibrational energy. However, a recent study showed that prominently chemisorbed diatomic radicals (e.g., OH) possess a significant vibrational free energy of 100 meV at room temperature.…”