Charge Density and Bonding Properties of LaFeAsO under Pressure

Abstract

Some interesting aspects of the electronic structure of iron oxypnictides depend sensitively on pressure. We investigate this sensitive pressure dependence in the parent compound LaFeAsO by full-potential electronic structure calculations based on density functional theory. We evaluate the sensitivity of the electronic structure to the Fe–As bond length as being due to the rather high degree of covalency associated with the bond, by visualizing the charge density distributions in detail. A strong pressure dependence in the charge density distributions is observed in the two bands, that form cylindrical electron sheets of the Fermi surface at ambient pressure. The bonding states associated with the Fe and As atoms rapidly grow up to 4 GPa and gradually start to decrease above 4 GPa. These pressure dependences of the covalency for the Fe–As bond are similar to the observed pressure dependences in superconductive transition temperatures. It is suggested that this result play an important role in exploring the origin of the superconductivity of LaFeAsO.