Equilibrium ground-state properties of the ternary alkali metal coinage metal phosphides K2CuP and K2AgP: New insights from first principles calculations

Abstract

The purpose of this paper is to report on the hitherto unexplored physical properties of the ternary polar intermetallic phases K2MP (M = Cu, Ag), namely, the structural, elastic, electronic and optical properties, based on first-principles calculations. All explored properties are based on the semi-local GGA-PBE functional. In addition to the GGA-PBE, the band dispersions have been also treated within the nonlocal hybrid functional HSE06. The calculated ground state structure parameters agree very well with the available experimental data. The first theoretical estimations of the single crystal and polycrystalline elastic moduli are reported. The obtained results indicate that both studied materials will show rather weak stiffness. Band dispersions clearly reveal that the considered compounds are indirect moderate-band-gap semiconductors. Charge density difference maps, electron localization function and Mulliken charge analyses provide a convincing evidence of covalent M − P interactions, appreciable covalent interaction between the coinage metal atoms along the zigzag chains and ionic K–P bonding. A set of frequency-dependent linear optical functions is calculated for a wide photon energy range up to 15 eV. The obtained results show that the studied materials are active for a wide-ranging photon energy in the ultraviolet spectrum.