Research Projects

Vibrational spectroscopy offers valuable insights into chemical bonds, dynamics, and morphology of molecular systems. Accurate quantum mechanical calculations for molecular vibrations can provide valuable information and study potential energy surfaces (PESs), but they are computational bottlenecks. High-resolution experimental IR data are broadening the applicability of molecular systems with constraints, especially for large molecules. To develop accurate yet affordable computational methods, sufficiently accurate ab initio PESs with viable anharmonic vibrational algorithms are essential. Quantum mechanical VSCF is one suitable method for vibrational structure theory (VST), but not yet feasible for large systems. The accuracy of PES depends on the level of electronic structure theory (EST) used. Proper quantification of errors is required for better cost/accuracy ratio. This proposal aims to quantify the accuracy/error pattern of each segment of EST and VTS on anharmonic PES, develop accurate yet faster hybrid approaches for construction of anharmonic PES, and apply hybrid PESs for large molecules. The harmonic potential contributes a major part to spectra and requires highest accuracy for a given VST. Pure anharmonic correction is smaller in magnitude but highly significant to achieve superior accuracy, and can be treated by low-level methods. Multi-level methods, basis sets, and their combinations in EST can be developed for construction of hybrid PES with improved accuracy and efficiency. This new algorithm will offer a suitable state-of-the-art black-box protocol for calculations of anharmonic vibrational spectroscopy of large molecules.