Extending the Molecular Tailoring Approach for Reliable and Efficient Nuclear Magnetic Resonance Spectral Calculations

Computing nuclear magnetic resonance (NMR) spectral parameters at advanced levels of theory with large basis sets becomes increasingly challenging as the molecular size grows. Here, we propose an efficient fragment-based protocol for the accurate evaluation of NMR parameters for large molecular systems. The isotropic shielding tensors and spin-spin coupling constants are approximated from fragment runs, followed by the use of molecular tailoring approach (MTA). The MTA-based calculations at DFT/MP2 level on prototype medium-sized molecules in conjunction with the grafting procedure exhibit excellent agreement with the corresponding full conventional calculations. Furthermore, for selected test cases, the accuracy of the proposed methodology is assessed by comparison with experimental results. The accuracy and acceleration achieved through independent and parallel fragment calculations make this approach an affordable and practical tool for examining NMR features of large molecular systems using off-the-shelf hardware. The methodology becomes particularly valuable when standard ab initio codes fail to run or require huge computational resources for large molecular systems.