Abstract:
Ab initio calculations were performed for cubic Fm-3 m (225) and tetragonal (I4/m) phases for
Cs2AgBiBr6(CaB2). We used the Vienna Ab Initio Simulation Package (VASP) to calculate the ground state
properties using two different exchange-correlation functionals, namely the Generalized gradient
approximation method (GGA) and the screened hybrid functional as proposed by Heyd, Scuseria,
and Ernzerhof (HSE06) method. Tetragonal Cs2AgBiBr6 phase was stabilized in the tetragonal phase.
The bandgap (Eg) was calculated using HSE06 for the polymorphs optimized at the PBE level and it is
found that they belong to the indirect bandgap. The calculated bandgap for cubic and tetragonal phases
in HSE06 for Cs2AgBiBr6 were 1.97 eV, and 2.4 eV, respectively. The character of chemical bonding in CaB2
is discussed based on electronic structures, charge density, charge transfer, and bond overlap population
analyses.
