An extension of the embedded fragment method for calculations on molecular clusters is presented, which includes strong external magnetic fields. The approach is flexible, allowing for calculations at the Hartree–Fock, current-density-functional theory, Møller–Plesset perturbation theory, and coupled-cluster levels using London atomic orbitals. For systems consisting of discrete molecular subunits, calculations using London atomic orbitals can be performed in a computationally tractable manner for systems beyond the reach of conventional calculations, even those accelerated by resolution-of-the-identity or Cholesky decomposition methods. To assess the applicability of the approach, applications to water clusters are presented, showing how strong magnetic fields enhance binding within the clusters. However, our calculations suggest that, contrary to previous suggestions in the literature, this enhanced binding may not be directly attributable to strengthening of hydrogen bonding. Instead, these results suggest that this arises for larger field strengths as a response of the system to the presence of the external field, which induces a charge density build up between the monomer units. The approach is embarrassingly parallel and its computational tractability is demonstrated for clusters of up to 103 water molecules in triple-ζ basis sets, which would correspond to conventional calculations with more than 12 000 basis functions.

中文翻译：

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强磁场中分子的嵌入片段法

提出了用于分子簇计算的嵌入式碎片方法的扩展，其中包括强外部磁场。该方法非常灵活，允许在 Hartree–Fock、电流密度泛函理论、Møller–Plesset 微扰理论和使用伦敦原子轨道的耦合簇水平上进行计算。对于由离散分子亚基组成的系统，使用伦敦原子轨道的计算可以以一种计算上易于处理的方式进行，适用于超出常规计算范围的系统，即使是那些通过身份解析或 Cholesky 分解方法加速的系统。为了评估该方法的适用性，提出了对水团簇的应用，展示了强磁场如何增强团簇内的结合。然而，我们的计算表明，与文献中先前的建议相反，这种增强的结合可能不能直接归因于氢键的加强。相反，这些结果表明，这是由于系统对外场存在的响应而产生的较大场强，这会导致单体单元之间电荷密度的增加。该方法是令人尴尬的并行，其计算易处理性在三重 ζ 基组中证明了多达 103 个水分子的簇，这将对应于具有超过 12000 个基函数的常规计算。这些结果表明，这是由于系统对外部场存在的响应而产生的较大场强，这会导致单体单元之间电荷密度的增加。该方法是令人尴尬的并行，其计算易处理性在三重 ζ 基组中证明了多达 103 个水分子的簇，这将对应于具有超过 12000 个基函数的常规计算。这些结果表明，这是由于系统对外部场存在的响应而产生的较大场强，这会导致单体单元之间电荷密度的增加。该方法是令人尴尬的并行，其计算易处理性在三重 ζ 基组中证明了多达 103 个水分子的簇，这将对应于具有超过 12000 个基函数的常规计算。