Center for Computational Materials, Oden Institute for Computational Engineering and Sciences , The University of Texas at Austin , Austin , Texas 78712 , United States.
Department of Physics , The University of Texas at Austin , Austin , Texas 78712 , United States.
J Chem Theory Comput. 2019 Oct 8;15(10):5299-5307. doi: 10.1021/acs.jctc.9b00520. Epub 2019 Sep 4.
Using an implementation based on real-space wave functions, we perform GW calculations of the HOMO and LUMO energies of molecules and atoms in the GW100 set. Our main conclusions are as follows: (1) Different implementations of the GW approximation show much better agreements for HOMO (highest occupied molecular orbital) energies than for LUMO (lowest unoccupied molecular orbital) energies. The mean absolute differences between the results calculated with different pseudopotential codes range from 100 to 200 meV. For delocalized LUMOs, all-electron codes that use local orbital basis tend to predict much higher energies than those calculated with plane-wave basis or real-space methods. (2) The effects of semicore electrons in pseudopotentials can explain some of the large discrepancies between results calculated with different GW implementations. For molecules or atoms that include I, Xe, and Ga, pseudopotential-based calculations that exclude semicore electrons produce results that agree better with all-electron calculations. For polar molecules such as NaCl and BrK, however, it is necessary to include semicore electrons for alkaline metal elements to get correct LUMO energies. (3) More than 20 molecules show rearrangement of the order between LUMO (or HOMO) with other orbitals due to GW corrections. Such orbitals that switch order with LUMO are unbound and delocalized in space. The predicted LUMO GW levels (or electron affinity) can be corrected by 2.0 eV if we consider the rearrangement of orbitals in GW calculations. In all, our work clarifies some of the discrepancies between different GW codes and sets a benchmark for real-space implementations of the GW approximation.
我们使用基于实空间波函数的方法，对 GW100 分子和原子数据集的 HOMO 和 LUMO 能量进行 GW 计算。我们的主要结论如下：（1）GW 近似的不同实现方法对于 HOMO（最高占据分子轨道）能量的计算结果具有更好的一致性，而对于 LUMO（最低未占据分子轨道）能量的计算结果则差异较大。不同赝势代码计算的 HOMO 能量之间的平均绝对差异在 100 到 200 meV 之间。对于离域的 LUMO 轨道，使用局域轨道基组的全电子方法往往比平面波基组或实空间方法预测的能量更高。（2）赝势中的半芯电子对不同 GW 实现方法之间的结果差异有一定的解释作用。对于包含 I、Xe 和 Ga 等元素的分子或原子，排除半芯电子的赝势计算结果与全电子计算结果更为一致。然而，对于 NaCl 和 BrK 等极性分子，为了得到正确的 LUMO 能量，需要在碱性金属元素的计算中包含半芯电子。（3）超过 20 个分子的 LUMO（或 HOMO）能级与其他轨道之间的顺序由于 GW 修正而发生了重排。与 LUMO 发生能级交换的轨道是无定域的。如果我们考虑 GW 计算中轨道的重排，可以将预测的 LUMO GW 能级（或电子亲和能）修正到 2.0 eV。总的来说，我们的工作澄清了不同 GW 代码之间的一些差异，并为 GW 近似的实空间实现提供了基准。
