Blase Xavier, Boulanger Paul, Bruneval Fabien, Fernandez-Serra Marivi, Duchemin Ivan
CNRS, Institut NEEL, F-38042 Grenoble, France.
CEA, DEN, Service de Recherches de Métallurgie Physique, F-91191 Gif-sur-Yvette, France.
J Chem Phys. 2016 Jan 21;144(3):034109. doi: 10.1063/1.4940139.
We study within the GW and Bethe-Salpeter many-body perturbation theories the electronic and optical properties of small (H2O)n water clusters (n = 1-6). Comparison with high-level CCSD(T) Coupled-Cluster at the Single Double (Triple) levels and ADC(3) Green's function third order algebraic diagrammatic construction calculations indicates that the standard non-self-consistent G0W0@PBE or G0W0@PBE0 approaches significantly underestimate the ionization energy by about 1.1 eV and 0.5 eV, respectively. Consequently, the related Bethe-Salpeter lowest optical excitations are found to be located much too low in energy when building transitions from a non-self-consistent G0W0 description of the quasiparticle spectrum. Simple self-consistent schemes, with update of the eigenvalues only, are shown to provide a weak dependence on the Kohn-Sham starting point and a much better agreement with reference calculations. The present findings rationalize the theory to experiment possible discrepancies observed in previous G0W0 and Bethe-Salpeter studies of bulk water. The increase of the optical gap with increasing cluster size is consistent with the evolution from gas to dense ice or water phases and results from an enhanced screening of the electron-hole interaction.
我们在GW和Bethe-Salpeter多体微扰理论框架下研究了小尺寸(H2O)n水团簇（n = 1 - 6）的电子和光学性质。与单双（三）级别的高级CCSD(T)耦合簇以及ADC(3)格林函数三阶代数图示构建计算结果的比较表明，标准的非自洽G0W0@PBE或G0W0@PBE0方法分别显著低估了电离能约1.1 eV和0.5 eV。因此，当从非自洽的G0W0准粒子谱描述构建跃迁时，相关的Bethe-Salpeter最低光学激发能被发现位置过低。仅更新本征值的简单自洽方案显示出对Kohn-Sham起始点的弱依赖性，并且与参考计算结果有更好的一致性。本研究结果解释了先前对体相水的G0W0和Bethe-Salpeter研究中理论与实验可能存在的差异。光学能隙随团簇尺寸增大而增加，这与从气相到致密冰或水相的演化一致，并且是电子 - 空穴相互作用屏蔽增强的结果。
