Abstract
We report the vibrational and thermodynamic properties of four known CsPbI3 polymorphs in the framework of the density functional theory. We compare the recently introduced strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) with the local density approximation (LDA). We found that the SCAN, compared to the LDA, could explain discrepancies between theoretical and experimental results. Evaluating the Helmholtz free energy as a function of temperature, we found that within the SCAN (a) all polymorphs had negative formation enthalpies at the room temperature and (b) CsPbI3 underwent the phase transition from the δ- to α-phase at 480 K. This is not true for the LDA. In contrast to the previous reports based on the LDA, we did not find the ferroelectric instability in the phonon spectra of the cubic and tetragonal phases at the meta-GGA level. This result agrees with the lack of observation of the ferroelectricity in CsPbI3.
Highlights
We report the vibrational and thermodynamic properties of four known CsPbI3 polymorphs in the framework of the density functional theory
In this work we show that in the case of CsPbI3 polymorphs the strongly constrained and appropriately normed (SCAN) functional leads to the more accurate description of their structural and vibrational properties and, as a result, the phase transitions compared to the other XC functionals
We found that meta-generalized gradient approximation (GGA) SCAN led to the better agreement with the experimental data for the values of the structural parameters than the local density approximation (LDA)
Summary
We report the vibrational and thermodynamic properties of four known CsPbI3 polymorphs in the framework of the density functional theory. For the β-CsPbI3, the Efor calculated within GGA and meta-GGA SCAN functionals is negative (−77 meV/f.u. and −64 meV/f.u., respectively), which indicates a stable phase.
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