We report the implementation of a cost-effective approximation method within the framework of the time-dependent optimized coupled-cluster (TD-OCC) method [T. Sato et al., J. Chem. Phys. 148, 051101 (2018)] for real-time simulations of intense laser-driven multielectron dynamics. The method, designated as TD-OCEPA0, is a time-dependent extension of the simplest version of the coupled-electron pair approximation with optimized orbitals [U. Bozkaya and C. D. Sherrill, J. Chem. Phys. 139, 054104 (2013)]. It is size extensive, gauge invariant, and computationally much more efficient than the TD-OCC method with double excitations. We employed this method to simulate the electron dynamics in Ne and Ar atoms exposed to intense near infrared laser pulses with various intensities. The computed results, including high-harmonic generation spectra and ionization yields, are compared with those of various other methods ranging from uncorrelated time-dependent Hartree–Fock to fully correlated (within the active orbital space) time-dependent complete-active-space self-consistent field (TD-CASSCF). The TD-OCEPA0 results show good agreement with TD-CASSCF ones for moderate laser intensities. For higher intensities, however, TD-OCEPA0 tends to overestimate the correlation effect, as occasionally observed for CEPA0 in the ground-state correlation energy calculations.

中文翻译：

---

基于时间的优化耦合簇方法，用于多电子动力学。二。耦合电子对近似

我们报告了在时间相关的优化耦合群集（TD-OCC）方法[T. 佐藤等。J.Chem。物理 148，051101（2018）]为强烈激光驱动多电子动力学实时仿真。命名为TD-OCEPA0的方法是具有优化轨道的最简单版本的耦合电子对逼近的时间依赖扩展。Bozkaya和CD Sherrill，化学杂志。物理 139，054104（2013）]。它比双激励的TD-OCC方法尺寸大，规格不变且计算效率高得多。我们采用这种方法来模拟暴露于各种强度的近红外激光脉冲的Ne和Ar原子中的电子动力学。计算结果，包括高次谐波产生谱和电离产率，与其他各种方法的结果进行了比较，从不相关的时间相关的Hartree-Fock到完全相关的（在活动轨道空间内）时间相关的完全活动空间自我-一致字段（TD-CASSCF）。TD-OCEPA0结果与TD-CASSCF的结果在中等激光强度上具有很好的一致性。但是，对于更高的强度，TD-OCEPA0倾向于高估相关效应，