Stability and hydrogen storage performance of Na2LiXH6 (X = Zr, V, Cr) double perovskite hydrides via DFT and AIMD

Abstract

This study aims to provide a comprehensive first-principles investigation, based on density functional theory (DFT) using the GGA-PBE functional, of Na₂LiXH₆ (X = Zr, V, Cr) double perovskite hydrides that crystallize in the Fmm (225) space group. The structural, electronic, optical, and thermodynamic properties were systematically explored to evaluate their potential for advanced hydrogen storage and clean energy applications. Phonon dispersion and ab initio molecular dynamics (AIMD) simulations confirm the dynamical and thermal stability of the system at 300 K, without any structural distortion. Among the investigated compounds, Na₂LiVH₆ shows the highest gravimetric capacity (5.50 wt%) and an optimal desorption temperature (540.23 K), favorable for reversible hydrogen release. Electronic analysis reveals metallic conductivity, while thermodynamic parameters, including heat capacity, enthalpy, entropy, and free energy, exhibit stable temperature-dependent trends. Collectively, these DFT-GGA-PBE results demonstrate that Na₂LiVH₆ possesses superior mechanical endurance, lattice stability, and multifunctional potential for next-generation hydrogen storage and sustainable energy applications.