Ramasimha Varma Arjun Varma, Paul Shilpa, Itale Anup, Pable Pranav, Tibrewala Radhika, Dodal Samruddhi, Yerunkar Harshal, Bhaumik Saurav, Shah Vaishali, Gururajan Mogadalai Pandurangan, Prasanna Tiramkudlu R S
Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India.
Department of Mathematics, Indian Institute of Technology Bombay, Mumbai 400076, India.
ACS Omega. 2023 Mar 13;8(12):11251-11260. doi: 10.1021/acsomega.2c08244. eCollection 2023 Mar 28.
In density functional theory (DFT)-based total energy studies, the van der Waals (vdW) and zero-point vibrational energy (ZPVE) correction terms are included to obtain energy differences between polymorphs. We propose and compute a new correction term to the total energy, due to electron-phonon interactions (EPI). We rely on Allen's general formalism, which goes beyond the quasi-harmonic approximation (QHA), to include the free energy contributions due to quasiparticle interactions. We show that, for semiconductors and insulators, the EPI contributions to the free energies of electrons and phonons are the corresponding zero-point energy contributions. Using an approximate version of Allen's formalism in combination with the Allen-Heine theory for EPI corrections, we calculate the zero-point EPI corrections to the total energy for cubic and hexagonal polytypes of carbon, silicon and silicon carbide. The EPI corrections alter the energy differences between polytypes. In SiC polytypes, the EPI correction term is more sensitive to crystal structure than the vdW and ZPVE terms and is thus essential in determining their energy differences. It clearly establishes that the cubic SiC-3C is metastable and hexagonal SiC-4H is the stable polytype. Our results are consistent with the experimental results of Kleykamp. Our study enables the inclusion of EPI corrections as a separate term in the free energy expression. This opens the way to go beyond the QHA by including the contribution of EPI on all thermodynamic properties.
在基于密度泛函理论（DFT）的总能研究中，包含范德华（vdW）和零点振动能（ZPVE）校正项以获得多晶型物之间的能量差。我们提出并计算了一个由于电子 - 声子相互作用（EPI）而产生的对总能的新校正项。我们依赖于艾伦的通用形式，它超越了准谐近似（QHA），以纳入由于准粒子相互作用产生的自由能贡献。我们表明，对于半导体和绝缘体，EPI对电子和声子自由能的贡献就是相应的零点能贡献。使用艾伦形式的近似版本并结合艾伦 - 海涅理论进行EPI校正，我们计算了碳、硅和碳化硅的立方和六方多型体总能的零点EPI校正。EPI校正改变了多型体之间的能量差。在SiC多型体中，EPI校正项比vdW和ZPVE项对晶体结构更敏感，因此在确定它们的能量差方面至关重要。它清楚地表明立方SiC - 3C是亚稳的，六方SiC - 4H是稳定的多型体。我们的结果与克莱坎普的实验结果一致。我们的研究使得能够将EPI校正作为自由能表达式中的一个单独项包含进来。这为通过纳入EPI对所有热力学性质的贡献来超越QHA开辟了道路。
