We show that accurate oscillator strengths can be obtained from adiabatic connection (AC) approaches based on the extended random phase approximation (ERPA) combined with multireference (complete active space, CAS) wave functions. The oscillator strengths calculated using the perturbation-corrected ERPA transition density matrices, proposed in this work, and the excitation energies calculated with recently introduced AC correlation energy methods, AC0 and AC0D, compete with accuracy in the perturbational CASPT2 approach and require less computational effort. AC0 and AC0D methods scale more favorably with the number of active orbitals than multiconfigurational perturbation approaches like CASPT2 and NEVPT2 thanks to their dependence on reduced density matrices up to the order of 2. Importantly, the newly developed approach for computing correlated transition dipole moments does not entail any additional costs, as all intermediate quantities become available when AC0 energies are being computed. We also test the performance of the recently proposed AC method corrected for the negative-transition contributions to the correlation energy, AC0D, for triplet excitation energies. Similarly, as for the singlet excitations, the correction improves the performance of the AC0 method, particularly for the low-lying excited states.

中文翻译：

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基于扩展随机相位近似的绝热连接方法的多参考相关振荡器强度


我们证明，可以通过基于扩展随机相位近似（ERPA）与多参考（完整活动空间，CAS）波函数相结合的绝热连接（AC）方法获得准确的振荡器强度。使用本文提出的扰动校正 ERPA 跃迁密度矩阵计算的振荡器强度，以及使用最近引入的 AC 相关能量方法 AC0 和 AC0D 计算的激发能量，可与扰动 CASPT2 方法的精度相媲美，并且需要较少的计算量。 AC0 和 AC0D 方法比 CASPT2 和 NEVPT2 等多配置扰动方法更能随活性轨道的数量进行缩放，因为它们依赖于高达 2 数量级的约化密度矩阵。重要的是，新开发的用于计算相关跃迁偶极矩的方法并不需要任何额外的成本，因为在计算 AC0 能量时所有中间量都可用。我们还测试了最近提出的 AC 方法的性能，该方法针对三重态激发能的相关能量 AC0D 的负跃迁贡献进行了校正。类似地，对于单重态激发，校正提高了 AC0 方法的性能，特别是对于低位激发态。