Significant impact of quantum and anharmonic effects on the structural stability and superconductivity of NbH3 at high pressures

Abstract

First-principles calculations combined with the stochastic self-consistent harmonic approximation reveal significant effects of the quantum ionic fluctuations and lattice anharmonicity on the structural stability and superconducting properties of NbH3 under high pressure. Previous theoretical predictions, which ignored ionic fluctuations and relied on the harmonic approximation, predicted the I4¯3d phase as the ground state between 33 and 400 GPa, with the Fm3¯m phase considered thermodynamically metastable. Harmonic calculations also placed the minimum pressure for dynamical stability of the Fm3¯m phase as high as 290 GPa. However, recent experiments identified the Fm3¯m phase at 187 GPa. Contrasting these predictions, our study reveals that the Fm3¯m phase remains dynamically stable down to at least 145 GPa—approximately 145 GPa lower than harmonic estimates. Furthermore, while the I4¯3d phase is dynamically stable, it exhibits higher enthalpy than the Fm3¯m phase at 187 GPa, aligning with the experimental observations. We systematically investigate the structural, vibrational, and superconducting properties of the Fm3¯m NbH3 under pressures ranging from 100 to 300 GPa, uncovering substantial modifications induced by the quantum and anharmonic effects. The calculated superconducting critical temperature (Tc) from the McMillan equation (with μ*=0.15) for Fm3¯m NbH3 at 187 GPa is 44 K, close to the measured value. These findings highlight the crucial role of quantum anharmonic effects in shaping the structural and vibrational properties of NbH3 at high pressures.

Source-reported materials — not catalogue approval

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