Molecular-group-assisted chemical precompression in superconducting molecular hydride NaNH₁₆

Compressed hydrides have emerged as exemplary materials for high-temperature superconductivity, yet their experimental accessibility remains constrained by extreme pressure requirements (> 150 GPa) for obtaining atomic hydrogen structures. Here, we propose a strategy of incorporating the ammonium (NH_4) group into the molecular hydride NaH_12 framework to enhance the chemical precompression effect and reduce the external pressure required for the stable structure. The resulting molecular hydride R3-NaNH_16 remains stable at a relatively low pressure of 20 GPa while preserving a high superconducting transition temperature of 54.5 K. Our first-principles calculations show that the added NH_4^+0.45 cation effectively regulates the charge distribution of surrounding hydrogen molecules, adjusting the hydrogen sublattice interactions through the hydrogen bond network, and forming a pseudo-binary hydrogen lattice. Compared with the parent NaH_12, R3-NaNH_16 exhibits stronger chemical precompression effects and structural stability at lower pressures. Further electron-phonon coupling analysis indicates that the bending vibrations of NH_4 and the translational-rotational modes of H_2 molecular units scatter nearly free electrons near the Fermi level, thereby forming Cooper pairs. Our results demonstrate that molecular doping into molecular hydrides to enhance chemical precompression provides a viable pathway to realize high superconductivity at low pressures.