On the Electride Nature of Na-hP4
Abstract
Early quantum mechanical models suggested that pressure drives solids towards free-electron metal behavior where the ions are locked into simple close-packed structures. The prediction and subsequent discovery of high-pressure electrides (HPEs), compounds assuming open structures where the valence electrons are localized in interstitial voids, required a paradigm shift. Our quantum chemical calculations on the iconic insulating Na-hP4 HPE show that increasing density causes a 3s -> 3pd electronic transition due to Coulomb repulsion between the 1s2s and 3s states, and orthogonality of the 3pd states to the core. The large lobes of the resulting Na-pd hybrid orbitals point towards the center of an 11-membered penta-capped trigonal prism and overlap constructively, forming multi-centered bonds, which are responsible for the emergence of the interstitial charge localization in Na-hP4. These multi-centered bonds facilitate the increased density of this phase, which is key for its stabilization under pressure.
Keywords
Cite
@article{arxiv.2311.01601,
title = {On the Electride Nature of Na-hP4},
author = {Stefano Racioppi and Christian V. Storm and Malcolm I. McMahon and Eva Zurek},
journal= {arXiv preprint arXiv:2311.01601},
year = {2023}
}