2026/07/22 by Gajendra Bohara, Ramakrishna Podila
#cond-mat.mtrl-sci
Lattice dynamics are widely invoked in the design of solid electrolytes, yet phonon information is commonly compressed into a band center or another scalar softness measure. Here we test whether the complete lithium-projected phonon density of states (Li-PDOS) provides a reproducible descriptor of experimental room-temperature ionic conductivity. MatterSim forces and Phonopy were used to generate harmonic total and Li-projected spectra for crystallographically resolved entries in the OBELiX dataset. A composition and structure audit defined a primary cohort of 260 materials (212 train and 48 test), a strict cohort of 241, and an exact-composition cohort of 168. Across 20 independently generated phonon-calculation database comparisons, the mean Wasserstein-1 distance was 0.542 THz for total DOS and 0.731 THz for Li-PDOS, revealing broad agreement but systematic, projection-dependent softening. Higher conductivity was associated with redistribution of normalized Li spectral weight toward low frequencies: in the untouched test set, the Li fractions below 2 and 5 THz had Spearman coefficients of 0.333 and 0.374, while the 5% cumulative-frequency quantile had a coefficient of -0.393. A Wasserstein kernel on the full Li-PDOS achieved held-out R2=0.444, compared with 0.012 for total DOS and 0.181 for a static composition--structure kernel. The Li model remained stable in the strict (R2=0.462) and exact (R2=0.451) cohorts. Family adjustment attenuated scalar associations, and Li-versus-total whole-spectrum dependence was cohort sensitive. The results therefore support mobile-ion-resolved spectral distributions as useful comparative screening descriptors, not as a universal causal softness law.