Abstract
We develop a first-principles approach for the treatment of vibronic interactions in solids that overcomes the main limitations of state-of-the-art electron-phonon coupling formalisms. In particular, anharmonic effects in the nuclear dynamics are accounted to all orders via ab initio molecular dynamics simulations. This non-perturbative, self-consistent approach evaluates the response of the wave functions along the computed anharmonic trajectory; thus it fully considers the coupling between nuclear and electronic degrees of freedom. We validate and demonstrate the merits of the concept by calculating temperature-dependent, momentum-resolved spectral functions for silicon and the cubic perovskite SrTiO3, a strongly anharmonic material featuring soft modes. In the latter case, our approach reveals that anharmonicity and higher-order vibronic couplings contribute substantially to the electronic-structure at finite-temperatures, noticeably affecting band gaps and effective masses, and hence macroscopic properties such as transport coefficients.
Highlights
Electronic band structures are a fundamental concept in material science used to qualitatively understand and quantitatively assess optical and electronic properties of materials, e.g., charge carrier mobilities and absorption spectra of semiconductors
Such perturbative calculations rely on two approximations. (a) The nuclear motion is approximated in a harmonic model which is equivalent to the concept of phonons, and (b) the vibronic interaction between electronic and nuclear degrees of freedom is treated by perturbation theory in terms of electron-phonon coupling
We show that our approach reproduces harmonic data for supercells with atoms (Si), for which the perturbative Allen-Heine approach performs well, and we present temperature-dependent spectral functions, band gaps, and effective masses for cubic SrTiO3
Summary
Electronic band structures are a fundamental concept in material science used to qualitatively understand and quantitatively assess optical and electronic properties of materials, e.g., charge carrier mobilities and absorption spectra of semiconductors. Three pivotal advancements have paved the way towards predictive, quantitative ab initio calculations of electronic band structures: Advances in relativistic approaches [1], improvements in the treatment of electronic exchange and correlation [2,3], and the inclusion of electron-phonon interactions via perturbative many-body formalisms based on the Allen-Heine theory [4] The latter approach has been widely used to calculate temperaturedependent effects on the electronic structure stemming from nuclear motion [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]. We compute temperature-dependent spectral functions, band gaps, and effective masses for cubic SrTiO3, a prototypical perovskite In this case, the highly anharmonic dynamics [32,33] associated with the octahedral tilting typically observed in perovskites [34,35] results in a breakdown of the perturbative model and in significant changes in the electronic properties.
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