基于波函数理论的颜色中心能量的精确与收敛计算
Accurate and convergent energetics of color centers by wavefunction theory
AI总结：
本文提出一种基于CASSCF与NEVPT2波函数理论的从头算方法，用于精确计算金刚石NV⁻色心缺陷的能量、性质及几何结构，并通过团簇收敛研究定量重现完整能谱、Jahn-Teller畸变效应、精细结构及零声子线压力依赖性。
摘要：
半导体中点缺陷的从头算描述长期以来是密度泛函理论（DFT）方法面临的理论挑战，这类缺陷以具有显著多行列式特征的带隙内态为特点。在本研究中，我们设计了一种基于波函数理论（WFT）的从头算方法，作为一种具有竞争力的替代方案。具体而言，我们在缺陷局域多体波函数（CASSCF 层级）之上应用微扰理论（NEVPT2 层级），分别对动态和静态关联效应提供平衡的描述。这种量子化学方法在本研究以金刚石中的 NV$^-$ 中心为例进行展示，不仅用于能量和性质的计算，还用于几何优化，且针对每个电子态分别进行。通过弛豫尺寸逐渐增大的团簇模型并研究收敛行为，我们定量重现了：（i）NV$^-$ 的完整能谱，包括最近表征的高能态；（ii）Jahn-Teller 畸变对可测量性质的影响；（iii）基态和激发态的精细结构；（iv）零声子线的压力依赖性。我们的研究结果表明，将传统的基于波函数的量子化学方法应用于精心构建的团簇上，可以成为讨论缺陷态能量学的一种稳健的常规工具。
英文摘要：
Ab initio description of point defects in semiconductors, characterized by in-gap states of significant multideterminant character, presents a longstanding theoretical challenge for density functional theory (DFT) methods. In this study, we devise a wavefunction theory (WFT) based ab initio methodology as a competing alternative approach. Specifically, we apply perturbation theory (NEVPT2 level) on top of a defect-localized many-body wavefunction (CASSCF level), which provides a balanced description of dynamic and static correlation effects, respectively. This quantum chemical methodology, exemplified for the NV$^-$ center in diamond in this study, is not only used for the calculation of energies and properties, but also for geometry optimization, performed for each electronic state individually. By relaxing cluster models of increasing size and investigating convergence behavior, we quantitatively reproduce (i) the full energy spectrum of NV$^-$ including the recently characterized high-energy states, (ii) the effect of Jahn-Teller distortion on measurable properties, (iii) the fine structure of ground and excited states, (iv) the pressure dependence of zero-phonon lines. Our findings showcase that applying conventional wave-function-based quantum chemistry on carefully crafted clusters can be a robust routine tool for discussing defect-state energetics.
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