Department of Chemistry, Graduate School of Science, Nagoya University, Furocho, Chikusa Ward, Nagoya, Aichi 464-8601, Japan.
Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furocho, Chikusa Ward, Nagoya, Aichi 464-8601, Japan.
J Chem Phys. 2023 Apr 21;158(15). doi: 10.1063/5.0143793.
Second-order N-electron valence state perturbation theory (NEVPT2) is an exactly size-consistent and intruder-state-free multi-reference theory. To accelerate the NEVPT2 computation, Guo and Neese combined it with the local pair-natural orbital (PNO) method using the projected atomic orbitals (PAOs) as the underlying local basis [Guo et al., J. Chem. Phys. 144, 094111 (2016)]. In this paper, we report the further development of the PNO-NEVPT2 method using the orthonormal and non-redundant localized virtual molecular orbitals (LVMOs) instead of PAOs. The LVMOs were previously considered to perform relatively poor compared to PAOs because the resulting orbital domains were unacceptably large. Our prior work, however, showed that this drawback can be remedied by re-forming the domain construction scheme using differential overlap integrals [Saitow et al., J. Chem. Phys. 157, 084101 (2022)]. In this work, we develop further refinements to enhance the feasibility of using LVMOs. We first developed a two-level semi-local approach for screening out so-called weak-pairs to select or truncate the pairs for PNO constructions more flexibly. As a refinement specific to the Pipek-Mezey localization for LVMOs, we introduced an iterative scheme to truncate the Givens rotations using varying thresholds. We assessed the LVMO-based PNO-NEVPT2 method through benchmark calculations for linear phenyl alkanes, which demonstrate that it performs comparably well relative to the PAO-based approach. In addition, we evaluated the Co-C bond dissociation energies for the cobalamin derivatives composed of 200 or more atoms, which confirms that the LVMO-based method can recover more than 99.85% of the canonical NEVPT2 correlation energy.
二阶 N 电子价层微扰理论 (NEVPT2) 是一种完全自洽且无侵入态的多参考理论。为了加速 NEVPT2 的计算，Guo 和 Neese 将其与局部对自然轨道 (PNO) 方法相结合，使用投影原子轨道 (PAO) 作为基础局部基 [Guo 等人，J. Chem. Phys. 144, 094111 (2016)]。在本文中，我们报告了使用正交且非冗余的局域虚拟分子轨道 (LVMO) 而不是 PAO 进一步开发 PNO-NEVPT2 方法。LVMO 之前被认为表现不如 PAO，因为得到的轨道域太大。然而，我们之前的工作表明，通过使用差分重叠积分重新形成域构建方案，可以克服这一缺点 [Saitow 等人，J. Chem. Phys. 157, 084101 (2022)]。在这项工作中，我们进一步改进了方法以提高使用 LVMO 的可行性。我们首先开发了一种两级半局部方法，用于筛选所谓的弱对，以便更灵活地选择或截断 PNO 构造的对。作为 LVMO 的 Pipek-Mezey 局域化的一种改进，我们引入了一种迭代方案，使用变化的阈值截断 Givens 旋转。我们通过对线型苯基链烷烃的基准计算评估了基于 LVMO 的 PNO-NEVPT2 方法，结果表明它的性能与基于 PAO 的方法相当。此外，我们评估了由 200 个或更多原子组成的钴胺素衍生物的 Co-C 键离解能，这证实了基于 LVMO 的方法可以恢复超过 99.85%的标准 NEVPT2 相关能量。
