Importance of Van der Waals Interactions in Hydrogen Adsorption on a Silicon-carbide Nanotube Revisited with vdW-DFT and Quantum Monte Carlo

Abstract

Density functional theory (DFT) is a valuable tool for calculating adsorption energies toward designing materials for hydrogen storage. However, dispersion forces being absent from the local/semi-local theory, it remains unclear as to how the consideration of van der Waals (vdW) interactions affects such calculations. For the first time, we applied diffusion Monte Carlo (DMC) to evaluate the adsorption characteristics of a hydrogen molecule on a (5,5) armchair silicon-carbide nanotube (H2-SiCNT). Within the DFT framework, we benchmarked various exchange-correlation functionals, including those recently developed for treating dispersion or vdW interactions. We found that the vdW-corrected DFT methods agree well with DMC, whereas the local (semilocal) functional significantly over (under)-binds. Furthermore, we fully optimized the H2-SiCNT geometry within the DFT framework and investigated the correlation between the structure and charge density. The vdW contribution to the adsorption was found to be non-negligible at ∼1 kcal/mol per hydrogen molecule, which amounts to 9–29% of the ideal adsorption energy required for hydrogen storage applications.

Interaction energy and isosteric heat of adsorption between hydrogen and magnesium diboride

“…Even though the analytical interaction energies fall in the desired range (∼15–48 kJ mol −1 ), 26 both isosteric heat of adsorption and first-principles binding energy calculations show low values (physisorption) between one gaseous H 2 molecule and all 5 studied terminated planes of MgB 2 . Considering these results in light of the high storage capacity that was experimentally witnessed on MgB 2 , we lean towards the postulate that H 2 dissociates subsequent to adsorption, followed by H atoms’ diffusion into the crystal lattice.…”

“…The focus on MgB 2 /Mg(BH) 4 as well as borohydrides for hydrogen storage has been discussed elsewhere with the key advantage being the potential for high gravimetric and volumetric storage densities as noted above. 6,[21][22][23][24][25] For hydrogen storage purposes, the interaction between hydrogen and an ideal sorbent material can be intuitively understood to have an optimal range (reportedly B15-48 kJ mol À1 by Prayogo et al), 26 where it is larger than physical adsorption for better retention at room temperature and smaller than chemisorption in order to allow low energy desorption. 27 A study from Ray et al in 2017 showed direct hydrogenation from MgB 2 to Mg(BH) 4 , which went through two steps: (1) dissociation of the H 2 molecule and (2) diffusive absorption initially from the high energy B-B bond.…”

DFT-D3 study of two-dimensional polymerization of C60 crystal under high pressure

“…Since van der Waals interactions affect distribution of electronic density, 45) the differences of approximation were investigated using the unit cells in Fig. 1.…”

Finite-Size Error Cancellation in Diffusion Monte Carlo Calculations of Surface Chemistry

“…Diffusion Monte Carlo (DMC), − a real-space, ground-state QMC method, has long been viewed as the gold standard for modeling the ground state properties of correlated solids due to its ability to accurately describe electron correlation. Previous work has established QMC as a highly accurate method for describing the properties of correlated solids, including transition metal oxides − and doped and/or defective materials. − More recent studies have demonstrated similar accuracies for covalent solids, especially materials involving van der Waals interactions, − encouraging DMC’s use in problems that require precise energy calculations, including heterogeneous catalysis. Furthermore, DMC has a comparatively low, polynomial ( O ( N 3 – N 4 ), where N is the number of electrons) cost compared to coupled cluster theory (CCSD­(T))- and full configuration interaction (FCI)-based methods. ,, …”