Zero-point lattice expansion and band gap renormalization: Gruneisen approach versus free energy minimization

Article

关键词: ANISOTROPIC THERMAL-EXPANSION;    TEMPERATURE-DEPENDENCE;    AB-INITIO;    PHOTOLUMINESCENCE SPECTRA;    ELECTRONIC-STRUCTURE;    ISOTOPIC MASS;    PARAMETERS;    PRESSURE;    COEFFICIENTS;    CONSTANTS;   

DOI  :  10.1103/PhysRevB.106.085137

来源: SCIE

【 摘 要 】

The zero-point lattice expansion (ZPLE) is a small variation of the lattice parameters induced by the presence of phonons in a material compared to the static lattice picture. It contributes significantly to the zero-point renormalization (ZPR) of the band gap energy, but its consequences have not been investigated as thoroughly as those stemming from electron-phonon interactions. In the usual first-principles approach, one evaluates the ZPLE by minimizing the T = 0 K Helmholtz free energy. In this work, we show that the formalism based on the Gruneisen parameters, which commonly neglects zero-point effects, can be efficiently used to compute the ZPLE for both isotropic and anisotropic materials at a much lower computational cost. We systematically test this formalism on 22 cubic and wurtzite materials, and we obtain excellent agreement with free energy minimization results for both the ZPLE and the resulting band gap ZPR. We use our results to validate an empirical expression estimating the ZPLE-induced ZPR, and we unveil its sensitivity to the temperature range involved in estimating the ZPLE from experimental data. Our findings finally reveal that the ZPLE contribution to the band gap ZPR can reach from 20% to more than 80% of the electron-phonon interaction contribution for heavier or more ionic materials, including materials containing light atoms. Considering both contributions on an equal footing is thus essential should one attempt to compare theoretical ZPR results with experimental data.

【 授权许可】

Free