Beijing National Laboratory for Molecular Sciences, Institute of Theoretical and Computational Chemistry, College of Chemistry, Peking University, 100871 Beijing, China.
J Chem Phys. 2011 May 28;134(20):204705. doi: 10.1063/1.3594205.
Early transition metal dichalcogenides (TMDC), characterized by their quasi-two-dimensional layered structure, have attracted intensive interest due to their versatile chemical and physical properties, but a comprehensive understanding of their structural and electronic properties from a first-principles point of view is still lacking. In this work, four simple TMDC materials, MX(2) (M = Zr and Hf, X = S and Se), are investigated by the Kohn-Sham density functional theory (KS-DFT) with different local or semilocal exchange-correlation (xc) functionals and many-body perturbation theory in the GW approximation. Although the widely used Perdew-Burke-Ernzelhof (PBE) generalized gradient approximation (GGA) xc functional overestimates the interlayer distance dramatically, two newly developed GGA functionals, PBE-for-solids (PBEsol) and Wu-Cohen 2006 (WC06), can reproduce experimental crystal structures of these TMDC materials very well. The GW method, currently the most accurate first-principles approach for electronic band structures of extended systems, gives the fundamental band gaps of all these materials in good agreement with the experimental values obtained from optical absorption. The minimal direct gaps from GW are systematically larger than those measured from thermoreflectance by about 0.1-0.3 eV, implying that excitonic effects may be stronger than previously estimated. The calculated density of states from GW quasi-particle band energies agrees very well with photo-emission spectroscopy data. Ionization potentials of these materials are also computed by combining PBE calculations based on the slab model and GW quasi-particle corrections. The calculated absolute band energies with respect to the vacuum level indicate that that ZrS(2) and HfS(2), although having suitable band gaps for visible light absorption, cannot be used for overall water splitting as a result of mismatch of the conduction band minimum with the redox potential of H(+)/H(2).
早期的过渡金属二卤化物（TMDC）具有准二维层状结构，由于其多样的化学和物理性质而引起了广泛关注，但从第一性原理的角度对其结构和电子性质的全面理解仍然缺乏。在这项工作中，使用 Kohn-Sham 密度泛函理论（KS-DFT）结合不同的局域或半局域交换相关（xc）泛函和 GW 近似中的多体微扰理论，研究了四种简单的 TMDC 材料 MX(2)（M = Zr 和 Hf，X = S 和 Se）。虽然广泛使用的 Perdew-Burke-Ernzelhof（PBE）广义梯度近似（GGA）xc 泛函极大地高估了层间距离，但两种新开发的 GGA 泛函，PBE-for-solids（PBEsol）和 Wu-Cohen 2006（WC06），可以很好地再现这些 TMDC 材料的实验晶体结构。GW 方法是目前扩展系统电子能带结构最准确的第一性原理方法，它给出的所有这些材料的基本带隙与从光学吸收获得的实验值非常吻合。GW 得到的最小直接带隙系统地比从热反射测量得到的要大 0.1-0.3 eV，这意味着激子效应可能比以前估计的要强。GW 准粒子能带能量的计算态密度与光发射谱数据非常吻合。还通过组合基于薄片模型的 PBE 计算和 GW 准粒子修正来计算这些材料的电离势。相对于真空能级的计算绝对能带能量表明，ZrS(2)和 HfS(2)虽然具有适合可见光吸收的带隙，但由于导带最小值与 H(+) / H(2)的氧化还原电位不匹配，不能用于整体水分解。
