First-Principles Study on Structural, Electronic, Mechanical, Optical, Vibrational, Thermal, And Hydrogen Storage Properties of Li2SnH4 and Na2SnH4 Compounds

Abstract

This study presents a comprehensive first-principles investigation of the structural, electronic, mechanical, vibrational, thermal, and hydrogen storage properties of X2SnH4 (X = Li and Na) hydrides in the tetragonal P42/mnm phase. Thermodynamic stability is confirmed by negative formation energies (−0.002 eV/atom for Li2SnH4 and –0.049 eV/atom for Na2SnH4), while phonon spectra without imaginary modes demonstrate dynamic stability. Electronic analyses reveal semiconducting behavior with band gaps of 0.678 eV (Li2SnH4) and 1.251 eV (Na2SnH4). Mechanical stability is verified by Born criteria, and Li2SnH4 exhibits higher stiffness (B = 59.0 GPa, G = 29.8 GPa) compared to Na2SnH4 (B = 38.3 GPa, G = 20.1 GPa). Vibrational and thermal results indicate stronger H–Sn bonding and higher lattice rigidity in Li2SnH4, supported by its larger Debye temperature (∼2300 K) relative to Na2SnH4 (∼1600 K). Hydrogen storage analysis yields gravimetric capacities of 5.95 wt% for Li2SnH4 and 4.82 wt% for Na2SnH4, highlighting their potential as lightweight hydrogen storage materials. Overall, the combined electronic, mechanical, thermal, and storage properties identify X2SnH4 compounds, particularly Li2SnH4, as promising candidates for next-generation solid-state hydrogen storage applications.