The Importance of Short- and Long-Range Exchange on Various Excited State Properties of DNA Monomers, Stacked Complexes, and Watson-Crick Pairs

TL;DR

This study evaluates various TD-DFT methods, emphasizing the necessity of both short- and long-range exchange components for accurately predicting diverse excited states in DNA nucleobases and their complexes.

Contribution

It demonstrates the critical role of non-empirically tuned long-range exchange in TD-DFT for modeling complex DNA excitations accurately.

Findings

Functionals lacking full exchange components perform poorly.

Both short- and long-range exchange are essential for accurate predictions.

Non-empirically tuned long-range exchange improves excitation energy accuracy.

Abstract

We present a detailed analysis of several time-dependent DFT (TD-DFT) methods, including conventional hybrid functionals and two types of non-empirically tuned range-separated functionals, for predicting a diverse set of electronic excitations in DNA nucleobase monomers and dimers. This large and extensive set of excitations comprises a total of 50 different transitions (for each tested DFT functional) that includes several n $\rightarrow$ {\pi} and {\pi} $\rightarrow$ {\pi}* valence excitations, long-range charge-transfer excitations, and extended Rydberg transitions (complete with benchmark calculations from high-level EOM-CCSD(T) methods). The presence of localized valence excitations as well as extreme long-range charge-transfer excitations in these systems poses a serious challenge for TD-DFT methods that allows us to assess the importance of both short- and long-range exchange contributions for simultaneously predicting all of these various transitions. In particular, we find that functionals that do not have both short- and full long-range exchange components are unable to predict the different types of nucleobase excitations with the same accuracy. Most importantly, the current study highlights the importance of both short-range exchange and a non-empirically tuned contribution of long-range exchange for accurately predicting the diverse excitations in these challenging nucleobase systems.