Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany.
J Chem Phys. 2018 Jan 21;148(3):031101. doi: 10.1063/1.5011204.
Electron correlation methods based on pair natural orbitals (PNOs) have gained an increasing degree of interest in recent years, as they permit energy calculations to be performed on systems containing up to many hundred atoms, while maintaining chemical accuracy for reaction energies. We present an approach for taking exact analytical first derivatives of the energy contributions in the simplest method of the family of Domain-based Local Pair Natural Orbital (DLPNO) methods, closed-shell DLPNO-MP2. The Lagrangian function contains constraints to account for the relaxation of PNOs. RI-MP2 reference geometries are reproduced accurately, as exemplified for four systems with a substantial degree of nonbonding interactions. By the example of electric field gradients, we demonstrate that omitting PNO-specific constraints can lead to dramatic errors for orbital-relaxed properties.
近年来，基于对键自然轨道（PNO）的电子相关方法引起了越来越多的关注，因为它们允许对包含多达数百个原子的系统进行能量计算，同时保持反应能量的化学准确性。我们提出了一种方法，可以对基于域的局部对键自然轨道（DLPNO）方法族中的最简单方法，即闭壳层 DLPNO-MP2 中能量贡献进行精确的解析一阶导数计算。拉格朗日函数包含约束条件，以考虑 PNO 的弛豫。准确地再现了 RI-MP2 参考几何形状，例如对于四个具有很大程度非键相互作用的系统进行了示例。通过电场梯度的例子，我们证明了省略特定于 PNO 的约束条件可能会导致轨道弛豫性质的显著误差。
