Accelerating Quantum Anharmonic Vibrational Calculations by Atom-Specific Hybrid Basis Set-Based Potential Energy...

The development of accurate yet fast quantum mechanical methods to calculate the anharmonic vibrational spectra of large molecules is one of the major goals of ongoing developments in this field. This study extensively explores and validates a hybrid electronic basis set approach for anharmonic vibrational calculations, where the molecule is segregated into different computational layers, and such layers are then treated with different levels of electronic basis sets. Following the system-bath model, the atoms corresponding to the active sites are treated in more accurate but computationally slower, large basis set and the rest of the atoms in less accurate but computationally faster, small basis set to construct the anharmonic hybrid potential energy surface (PES). Such a hybrid protocol for constructing an anharmonic PES is named as the atom-specific hybrid basis set (ASHBS) approach. The accuracy of the ASHBS approach is tested and established by evaluating the harmonic and anharmonic frequencies of a set of four prototype molecules. Following the ASHBS approach, for a chosen active site, the transitions of the corresponding modes are found to be closer to that of a high basis set, with a majority of target modes displaying a mean absolute error of around 3.3 cm^-1, while achieving the computational acceleration of 2-3 times. This study also provides insights into determining the optimal layer size to balance computational efficiency and accuracy, offering a suitable alternative, particularly for large molecules.