Structural, Vibrational, Elastic and Topological Properties of PaN Under Pressure

TL;DR

This study investigates the structural, vibrational, elastic, and topological properties of PaN under pressure using first principles methods, revealing a pressure-induced structural transition and contrasting predictions from different exchange-correlation functionals.

Contribution

It provides a detailed first-principles analysis of PaN under pressure, highlighting a potential topological transition predicted by GGA but absent in LDA and hybrid functionals.

Findings

PaN undergoes a structural transition near 58 GPa from NaCl to R-3m structure.

Anomalous behavior in phonon and elastic properties signals the structural transition.

GGA predicts a topological charge density transition, absent in LDA and hybrid functionals.

Abstract

Electronic, structural, vibrational and elastic properties of PaN have been studied both at ambient and high pressures, using first principles methods with several commonly used parameterizations of the exchange-correlation energy. The generalized gradient approximation (GGA) reproduces the ground state properties satisfactorily. Under pressure PaN is found to undergo a structural transition from NaCl to the R-3m structure near 58 GPa. The high pressure behavior of the acoustic phonon branch along the (1,0,0) and (1,1,0) directions, and the C44 elastic constant are anomalous, which signals the structural transition. With GGA exchange-correlation, a topological transition in the charge density occurs near the structural transition which may be regarded as a quantum phase transition, where the order parameter obeys a mean field scaling law. However, the topological transition is absent when other exchange-correlation functionals are invoked (local density approximation (LDA) and hybrid functional). Therefore, this constitutes an example of GGA and LDA leading to qualitatively different predictions, and it is of great interest to examine experimentally whether this topological transition occurs.