Table 1.

The calculated EPC parameter λ, the first moment of Eliashberg function $⟨\omega ⟩$, square root of the average square phonon frequencies $⟨{\omega }^2⟩$^1/2, logarithmic average frequency ω_log, DOS at Fermi level, and superconducting critical temperature T_c for MgP₂H₁₄, LiP₂H₁₄, BeP₂H₁₄, and NaP₂H₁₄ under pressure, T_c is obtained from solving the Allen-Dynes modified McMillan equation (herein, we default f₁f₂ = 1 when λ < 1) and isotropic Migdal Eliashberg equations, with the typical Coulomb pseudopotential μ^∗ = 0.10

System	P	λ	$⟨\omega ⟩$	$⟨{\omega }^2⟩$1/2	ωlog	N(Ef)	TcAD	f1f2TcAD	TcME	Reference
	(GPa)		(K)	(K)	(K)	(states/Ry/fu)	(K)	(K)	(K)
MgP2H14	280	1.65	1281	1481	1072	6.43	133	154	166	this work
	350	1.12	1691	1870	1464	6.43	120	130	–	this work
	400	1.02	1840	2030	1578	6.54	114	122	–	this work
NaP2H14	400	1.45	–	–	1101	6.28	139	–	159	Ref.10
BeP2H14	400	1.13	–	–	978	5.73	90	–	99	Ref.10
LiP2H14	400	0.85	–	–	1494	4.96	84	–	90	Ref.10
	300	1.06	–	–	1350	5.48	112	–	125	Ref.10
	230	1.69	–	–	956	6.08	143	–	169	Ref.10