4 years ago

Charge transfer excitations in TDDFT: A ghost-hunter index

Charge transfer excitations in TDDFT: A ghost-hunter index
Ilaria Ciofini, Giovanni Scalmani, Mike J. Frisch, Federica Maschietto, Carlo Adamo, Marco Campetella
This work presents a new index, MAC, enabling the on-the-fly detection of ghost charge transfer (CT) states, a major problem in time-dependent density-functional theory calculations. This computationally inexpensive index, derived as a modification of the Mulliken estimation of transition energy for CT excitations, relies on two basic ingredients: an effective CT distance, computed using our density-based index (DCT), and an orbital weighted estimation of the Ionization Potential and Electron Affinity. Some model systems, representative of both intermolecular and intramolecular CT excitations, were chosen as test cases. The robustness of our approach was verified by analyzing the behavior of functionals belonging to different classes (GGA, global hybrids and range separated hybrids). The results obtained show that ghost states are correctly spotted, also in the delicate case of intramolecular excitations displaying substantial donor-bridge-acceptor delocalization, in a regime for which the standard Mulliken formulation attends its limits. © 2017 Wiley Periodicals, Inc. A new index, MAC, enabling the on-the-fly detection of ghost charge transfer (CT) states in time dependent density functional theory is presented. It is derived by a simple combination of the Mulliken's formula for CT limiting energies and our density-based index (DCT) for average electron-hole distance. The evaluation of MAC is computationally inexpensive and its use make “safer” the GGA and hybrids approaches in the evaluation of excited electronic states.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/jcc.24862

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