A Unified Strategy for the Chemically Intuitive Interpretation of Molecular Optical Response Properties

Abstract

Interpreting response properties such as the polarizability, optical rotation (OR), or hyperpolarizabilities is a complex task for which a uniform strategy would be desirable. We propose a response analysis procedure called the RespA approach with two interrelated schemes to describe molecular optical response properties in terms of natural response orbitals (NROs) and chemical fragment response for convenient elucidation of structure−(optical)property relationships. These quantities can be easily extracted from the frequency-dependent perturbed one-electron transition/current density matrix obtained from any quantum mechanical response function calculation. NROs provide the most compact representation of the virtual excitations occurring in the (hyper)scattering process. It is decomposed in hole and electron NRO pairs providing a simple exciton picture. For a chemist, it is natural to interpret a property by decomposing it into functional groups or fragment contributions. In this spirit, the response is partitioned into on-site and between-site fragment responses, allowing a property mapping into real space. The new RespA procedure was implemented and tested at the simplified time-dependent density functional theory (sTD-DFT) level enabling calculations for large systems. The RespA strategy is a method-independent route for the understanding of a wide variety of response properties. We showcase how the chemically intuitive RespA approach extracts easily structure−property relationships for the particularly difficult case of OR. As examples, we demonstrate how to enhance the OR of [5]helicene and norbornenone, provide an analysis of the change of the OR observed for camphor and fenchone, and finally investigate the case of a (P,P)-bis-helicenic 2,2′-bipyridine chiroptical switch.

Perspective on Simplified Quantum Chemistry Methods for Excited States and Response Properties

“…To provide a method-agnostic, chemically intuitive interpretation of molecular optical response properties, we introduced the RespA approach . This strategy includes two interrelated schemes that describe response properties in terms of newly introduced natural response orbitals (NROs) and chemical fragment response.…”

“…Fragment definitions for norbornenone as well as important on-site (red) and between-sites response (green for A < B and blue for A > B ) for the β zz component of the OR response tensor are also shown. Reprinted with permission from ref . Copyright 2020 American Chemical Society.…”

Plasmonic Circular Dichroism in Chiral Gold Nanowire Dimers

“…Individual Component Maps of Rotatory Strength (ICM-RS) Analysis Recently, an analysis tool of the absorption spectra derived from TDDFT simulation has been proposed [ 35 ], i.e., individual component maps of oscillatory strength (ICM-OS) plots, which allows one to investigate the connection between absorption and single-particle excitations (ICM-OS). This field is subject to intense research efforts, and there are currently many efforts to find a proper method to rationalize CD (or in general spectral features) obtained from response calculations [ 36 ]. The same approach has been extended from the oscillator strength to the rotator strength, so in an analogous way we defined individual component maps of rotatory strength (ICM-RS) plots [ 24 ] as analysis tools of chiro-optical linear response spectra derived from TDDFT simulations.…”

“…Recently, an analysis tool of the absorption spectra derived from TDDFT simulation has been proposed [ 35 ], i.e., individual component maps of oscillatory strength (ICM-OS) plots, which allows one to investigate the connection between absorption and single-particle excitations (ICM-OS). This field is subject to intense research efforts, and there are currently many efforts to find a proper method to rationalize CD (or in general spectral features) obtained from response calculations [ 36 ].…”

All-Atom Quantum Mechanical Calculation of the Second-Harmonic Generation of Fluorescent Proteins

“…In this Letter, we propose a new all-atom QM methodology to generally compute β for FPs. This is now possible because of two recent developments and implementations: the GFN2-xTB method to optimize geometries with the program and the evaluation of quadratic response functions with the simplified time-dependent density functional theory (sTD-DFT) − and in particular its tight-binding version (sTD-DFT-xTB) available in the free program . The geometry of large proteins can now be optimized fully quantum mechanically before computing their β values , with modest CPU requirements.…”