Mei Yuncai, Li Chen, Su Neil Qiang, Yang Weitao
Department of Chemistry , Duke University , Durham , North Carolina 27708 , United States.
Key Laboratory of Theoretical Chemistry of Environment, School of Chemistry and Environment , South China Normal University , Guangzhou 510006 , China.
J Phys Chem A. 2019 Jan 24;123(3):666-673. doi: 10.1021/acs.jpca.8b10380. Epub 2019 Jan 10.
Quasiparticle energies and fundamental band gaps in particular are critical properties of molecules and materials. It was rigorously established that the generalized Kohn-Sham HOMO and LUMO orbital energies are the chemical potentials of electron removal and addition and thus good approximations to band edges and fundamental gaps from a density functional approximation (DFA) with minimal delocalization error. For other quasiparticle energies, their connection to the generalized Kohn-Sham orbital energies has not been established but remains highly interesting. We provide the comparison of experimental quasiparticle energies for many finite systems with calculations from the GW Green function and localized orbitals scaling correction (LOSC), a recently developed correction to semilocal DFAs, which has minimal delocalization error. Extensive results with over 40 systems clearly show that LOSC orbital energies achieve slightly better accuracy than the GW calculations with little dependence on the semilocal DFA, supporting the use of LOSC DFA orbital energies to predict quasiparticle energies. This also leads to the calculations of excitation energies of the N-electron systems from the ground state DFA calculations of the ( N - 1)-electron systems. Results show good performance with accuracy similar to TDDFT and the delta SCF approach for valence excitations with commonly used DFAs with or without LOSC. For Rydberg states, good accuracy was obtained only with the use of LOSC DFA. This work highlights the pathway to quasiparticle and excitation energies from ground density functional calculations.
准粒子能量，尤其是基本带隙，是分子和材料的关键性质。已经严格确定，广义Kohn-Sham最高已占分子轨道（HOMO）和最低未占分子轨道（LUMO）的轨道能量是电子去除和添加的化学势，因此从具有最小离域误差的密度泛函近似（DFA）来看，是对带边和基本带隙的良好近似。对于其他准粒子能量，它们与广义Kohn-Sham轨道能量的联系尚未确立，但仍然非常有趣。我们将许多有限体系的实验准粒子能量与GW格林函数和局域轨道标度校正（LOSC，一种最近开发的对半局域DFA的校正，具有最小离域误差）的计算结果进行了比较。对40多个体系的大量结果清楚地表明，LOSC轨道能量的精度略高于GW计算，且对半局域DFA的依赖性很小，这支持使用LOSC DFA轨道能量来预测准粒子能量。这也导致了从（N - 1）电子体系的基态DFA计算中计算N电子体系的激发能。结果表明，对于价激发，使用常用的有或没有LOSC的DFA时，其精度与含时密度泛函理论（TDDFT）和δ自洽场（delta SCF）方法相似，表现良好。对于里德堡态，只有使用LOSC DFA才能获得良好的精度。这项工作突出了从基态密度泛函计算获得准粒子和激发能的途径。
