Metrics for Molecular Electronic Excitations: A Comparison between Orbital- and Density-Based Descriptors

J Phys Chem A. 2017 Oct 12;121(40):7543-7549. doi: 10.1021/acs.jpca.7b07080. Epub 2017 Sep 27.

Abstract

This study proposes a quantitative and qualitative comparison of two popular metrics used for time-dependent density functional simulations of chromophores when describing absorption and emission processes, with high discrimination power between short- and long-range character of involved electronic excitations and functional performances. To this end, a total of 160 absorption and emission electronic excitations of 80 molecular systems belonging to the "Real-Life Molecules" data set, recently introduced in literature, have been considered a relevant data set. The two selected indexes are based on density (the DCT one) and natural transition orbitals (the ΔrNTO one), respectively. For comparison purposes, an extension of the DCT index, in line with what exists for ΔrNTO, enabling to discriminate electronic transitions occurring in symmetric systems is also proposed. The results show that, independently of the exchange and correlation functional used, a good correlation between the natural transition orbital and density based descriptors is found, thus cross validating their use for the quantification of a large variety of transitions in chemically relevant molecular systems.