Accurate quantum chemical methods for the prediction of spin-state energy gaps for strongly correlated systems are computationally expensive and scale poorly with the size of the system. This makes calculations for many experimentally interesting molecules impractical even with abundant computational resources. In previous work, we have shown that the localized active space (LAS) self-consistent field (SCF) method is an efficient way to obtain multi-configuration SCF wave functions of comparable quality to the corresponding complete active space (CAS) ones. To obtain quantitative results, a post-SCF method is needed to estimate the complete correlation energy. One such method is multiconfiguration pair-density functional theory (PDFT), which calculates the energy based on the density and on-top pair density obtained from a multiconfiguration wave function. In this work we introduce localized-active-space pair-density functional theory, which uses a LAS wave function for subsequent PDFT calculations. The method is tested for computing spin-state energy gaps in conjugated organic molecules and bimetallic compounds and is shown to give results within 0.05 eV of the corresponding CAS-PDFT results at a significantly lower cost.

中文翻译：

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局部主动空间对密度泛函理论

用于预测高度相关的系统的自旋能隙的精确量子化学方法在计算上昂贵，并且随系统规模的扩展而变差。即使有足够的计算资源，这也使得许多实验上有趣的分子的计算不切实际。在先前的工作中，我们已经表明，局部活动空间（LAS）自洽场（SCF）方法是一种获得质量与相应完整活动空间（CAS）相当的多配置SCF波函数的有效方法。为了获得定量结果，需要后SCF方法来估计完整的相关能量。一种这样的方法是多配置对密度泛函理论（PDFT），它根据从多配置波函数获得的密度和顶对密度计算能量。在这项工作中，我们介绍了局部活动空间对密度泛函理论，该理论使用LAS波函数进行后续PDFT计算。测试了该方法用于计算共轭有机分子和双金属化合物中的自旋态能隙，结果表明该方法以相对较低的成本提供了与相应CAS-PDFT结果相差0.05 eV的结果。