Assessing computationally efficient isomerization dynamics: Delta-SCF density-functional theory study of azobenzene molecular switching

TL;DR

This study compares Delta-SCF DFT, TD-DFT, and RI-CC2 methods for modeling azobenzene's isomerization, showing Delta-SCF's efficiency and robustness, making it promising for larger systems despite some limitations in excitation energy accuracy.

Contribution

It demonstrates that Delta-SCF DFT provides reliable PES topologies for azobenzene, comparable to more computationally intensive methods, highlighting its potential for studying larger molecular switches.

Findings

All three methods agree on PES topologies and match experimental data.

Delta-SCF and TD-DFT produce similar results for S1 and S2 with the same functional.

Delta-SCF is robust against state crossings and computationally efficient.

Abstract

We present a detailed comparison of the S0, S1 (n -> \pi*) and S2 (\pi -> \pi*) potential energy surfaces (PESs) of the prototypical molecular switch azobenzene as obtained by Delta-self-consistent-field (Delta-SCF) Density-Functional Theory (DFT), time-dependent DFT (TD-DFT) and approximate Coupled Cluster Singles and Doubles (RI-CC2). All three methods unanimously agree in terms of the PES topologies, which are furthermore fully consistent with existing experimental data concerning the photo-isomerization mechanism. In particular, sum-method corrected Delta-SCF and TD-DFT yield very similar results for S1 and S2, when based on the same ground-state exchange-correlation (xc) functional. While these techniques yield the correct PES topology already on the level of semi-local xc functionals, reliable absolute excitation energies as compared to RI-CC2 or experiment require an xc treatment on the level of long-range corrected hybrids. Nevertheless, particularly the robustness of Delta-SCF with respect to state crossings as well as its numerical efficiency suggest this approach as a promising route to dynamical studies of larger azobenzene-containing systems.