Computational Spectroscopy of Large Molecules by Fragmentation Methods

Abstract

Molecules-in-molecules (MIM) is a general fragment-based multi-layer approach for calculating accurate total energies and energy-derivatives of large molecules, similar in spirit to the popular ONIOM methodology. The MIM approach has recently been adapted for the efficient calculation of several spectroscopic properties such as infrared (MIM-IR), Raman (MIM-Raman), vibrational circular dichroism (MIM-VCD), Raman optical activity (MIM-ROA) and Nuclear Magnetic Resonance (MIM-NMR) spectra for large molecules. The relevant higher energy derivatives from smaller fragments are used to build the property tensors of the parent molecule leading to an efficient implementation of the relevant spectroscopic property tensors in the global coordinate frame of the large molecule. The incorporation of the Jacobian link atom projection method as well as the employment of multiple layers of theory in accounting for weak long-range interactions, are both critical factors that contribute to the accuracy of the resulting methods. Moreover, the solvation environment is incorporated in these MIM-Solvent spectroscopic calculations, either through explicit-, implicit-, or a combination of both solvation models. The proposed MIM fragment-based method is computationally cost-effective and provides a substantial speedup relative to conventional whole molecule calculations. This chapter presents the accuracy and performance of the MIM fragment-based method for evaluating vibrational, chiroptical, and NMR spectra of large benchmark molecules.