Electronic structure and excitations in oligoacenes from ab initio calculations

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Oligoacenes are polycyclic aromatic hydrocarbons with potential applications in organic electronics.
• Accurate theoretical prediction of their electronic properties is crucial for material design.

Purpose of the Study:

• To investigate the electronic properties of oligoacenes (C(4n+2)H(2n+4), n=2-6) using various ab initio methods.
• To evaluate the accuracy of Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) for predicting ionization potentials, electron affinities, and electronic excitations in oligoacenes.

Main Methods:

• Geometry optimization and electronic property calculations using Density Functional Theory (DFT).
• Computation of vertical and adiabatic ionization potentials and electron affinities via DFT.
• Calculation of low-lying electronic excitations using TD-DFT, Configuration Interaction Singles (CIS), and CIS(D).

Main Results:

• DFT-optimized geometries show good agreement with experimental data.
• Standard DFT exchange-correlation functionals systematically underestimate ionization potentials in oligoacenes.
• TD-DFT with standard functionals significantly underestimates the lowest singlet-singlet electronic transition energy.

Conclusions:

• Standard DFT functionals are insufficient for accurate prediction of ionization potentials and electronic excitations in oligoacenes.
• Further investigation into the reasons for underestimation by DFT functionals is warranted.
• Advanced computational methods may be required for precise characterization of oligoacene electronic behavior.