Ab Initio Investigation of the Physical Properties of Pb-Rich Compounds Pb2X (X = Rh, Pd, and Au)

Abstract

In this study, detailed physical properties including electronic, elastic, mechanical, phonon, and electron–phonon interaction properties of three Pb-rich compounds Pb₂X (X = Rh, Pd, and Au) have been researched by performing scalar relativistic and full relativistic ab initio pseudopotential calculations based on density functional theory with its generalized gradient approximation. A comparison of scalar relativistic and full relativistic results reveals that the existence of Pb 6p electrons at the Fermi level increases with the enhanced mass of the X element in Pb₂X compounds, making the effect of spin–orbit coupling on their physical properties more pronounced because Pb 6p electrons are well-known to have a strong spin–orbit interaction. In particular, when spin–orbit coupling is taken into account, the electron–phonon interaction in all the examined compounds becomes stronger with being the strongest for Pb₂Au. As a consequence, the calculation neglecting spin–orbit coupling underestimates the superconducting transition temperatures of the examined compounds, while the calculation including spin–orbit coupling improves the accordance with experiment satisfactorily, signaling the necessity of this coupling in determining the physical properties of the three Pb-rich compounds Pb₂X.