A new index is defined with the aim of further exploring the metric of excited electronic states in the framework of the time-dependent density functional theory. This descriptor, called Δr, is based on the charge centroids of the orbitals involved in the excitations and can be interpreted in term of the hole−electron distance. The tests carried out on a set of molecules characterized by a significant number of charge-transfer excitations well illustrate its ability in discriminating between short (Δr ≤ 1.5 Å) and long-range (Δr ≥ 2.0 Å) excitations. On the basis of the well-known pitfalls of TD-DFT, its values can be then associated to the functional performances in reproducing different type of transitions and allow for the definition of a “trust radius” for GGA and hybrid functionals. The study of other systems, including some well-known difficult cases for other metric descriptors, gives further evidence of the high discrimination power of the proposed index. The combined use with other density or orbital-based descriptors is finally suggested to have a reliable diagnostic test of TD-DFT transitions.
|Autori:||Ciro A. Guido;Pietro Cortona;Benedetta Mennucci;Carlo Adamo|
|Titolo:||On the Metric of Charge Transfer Molecular Excitations: A Simple Chemical Descriptor|
|Anno del prodotto:||2013|
|Digital Object Identifier (DOI):||10.1021/ct400337e|
|Appare nelle tipologie:||1.1 Articolo in rivista|