Chemical Precompression and Key Superconducting Indicators in High-Pressure XH _<i>n</i> Hydrides

Since the discovery of high-temperature superconductivity in CaH6, hydrogen-based superconductors have attracted great interest. This study focused on XHn (n = 4, 6) systems, where X = Mg, Ca, Sc, Y, and systematically evaluates superconductivity-related parameters under pressure. The vibrational energy of hydrogen units (EH) was first introduced as an indicator of structural stability. Additionally, two types of chemical templates were identified in metals hydrides near the “s-d” instability region, using s-d orbital electron transitions as a criterion, to explore the role of chemical precompression in stabilizing hydrides. The gray correlation analysis method is used to fit Tc and related factors. The primary and secondary relationships between parameters ELF value in the interstitial sites after hydrogenation (E2), EH, ωD, pressure and Tc in the XH6 system are investigated for the first time on the basis of high fitting accuracy. Ultimately, ωD and E2 are identified as key indicators of superconducting performance. These findings provide new insights into the mechanisms of stability and high-temperature superconductivity in pressurized hydrides, offering theoretical guidance for the discovery of novel superconductors. Synopsis: This study investigates XHn (n = 4, 6; X = Mg, Ca, Sc, Y) hydrogen-based superconductors under pressure. Using hydrogen vibrational energy (EH) and s–d orbital transitions, structural stability and chemical precompression effects are analyzed. Gray correlation reveals ωD and E2 as key indicators of Tc, offering insights into high-temperature superconductivity mechanisms.