Specific features of the electronic structure and optical properties of KPb2Br5: DFT calculations and X-ray spectroscopy measurements

• DFT calculations of total and partial densities of states of KPb2Br5 are made.
• The valence band is formed mainly from contributions of Pb 6s and Br 4p states.
• Unoccupied Pb 6p states are the principal contributors to the conduction band.
• Electronic structure of KPb2Br5 is studied experimentally by XPS and XES methods.
• Calculations of the main optical characteristics of KPb2Br5 are performed.

Density functional theory (DFT) calculations are made in order to explore the total and partial densities of states of potassium dilead pentabromide, KPb2Br5, by using the augmented plane wave + local orbitals (APW + lo) method as incorporated in the WIEN2k package. The present calculations reveal that the principle contributors to the valence band of KPb2Br5 are the Pb 6s and Br 4p states contributing predominantly at the bottom and at the top of the band, respectively, while the bottom of the conduction band is formed mainly from contributions of the unoccupied Pb 6p states. The curves of total density of states derived by the present DFT calculations of KPb2Br5 are found to be in agreement with the experimental X-ray photoelectron valence-band spectrum of the compound studied. Comparison on a common energy scale of the X-ray emission bands representing the energy distribution of the valence Br p and K s states and the X-ray photoelectron valence-band spectrum of the KPb2Br5 single crystal indicate that the Br 4p and K 4s states contribute mainly at the top and in the upper portion of the valence band, respectively, being in agreement with data of the present DFT band-structure calculations of this compound. Principal optical characteristics of KPb2Br5, namely dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity are also studied by the DFT calculations.

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