Importance of van der Waals interactions in hydrogen adsorption on a silicon-carbide nanotube revisited with vdW-DFT and quantum Monte Carlo

TL;DR

This study demonstrates that van der Waals interactions significantly influence hydrogen adsorption energies on silicon-carbide nanotubes, with vdW-corrected DFT aligning well with diffusion Monte Carlo results, highlighting their importance in hydrogen storage material design.

Contribution

First application of diffusion Monte Carlo to hydrogen adsorption on silicon-carbide nanotubes, benchmarking vdW-corrected DFT methods against DMC for accurate energy predictions.

Findings

vdW interactions contribute about 1 kcal/mol to adsorption energy

vdW-corrected DFT agrees well with DMC results

Local functionals over- or under-bind significantly

Abstract

DFT is a valuable tool for calculating adsorption energies toward designing materials for hydrogen storage. However, dispersion forces being absent from the theory, it remains unclear 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 (H$_2$-SiCNT). Within the framework of density functional theory (DFT), we also 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 H$_2$-SiCNT geometry within the DFT framework and investigated the correlation between structure and charge density. The vdW contribution to adsorption was found to be non-negligible at approximately 1 kcal/mol per hydrogen molecule, which amounts to 9-29 % of the ideal adsorption energy required for hydrogen storage applications.