Theoretical Study on the Exciton Binding Energy from Density Functional Theory Methods
Date Issued
2015
Date
2015
Author(s)
Lee, Jui-Che
Abstract
The exciton binding energy, the energy required to separate an excited electron-hole pair to free charge carriers, is one of the key performance factors of organic photoactive materials and devices. However, it is questionable whether modern quantum mechanical calculations based on the density functional theory (DFT) can provide reliable predictions for this physical quantity. In this study, we use two parts to discuss it. we compared the results from 9 common DFT methods, including LDA, PBE, M06L, B3LTP, ωB97, ωB97X, ωB97X-D, M06-HF, M06-2X, to the benchmark method, CCSD, for 121 small to medium sized molecules. The mean absolute errors in the exciton binding energy are found to be 0.38 eV from ωB97X, 0.39 from ωB97X, 0.40 eV from ωB97X-D, 0.48 eV from M06-2X, 0.53 eV from B3LYP, 0.57 eV from M06L, 0.66 eV from PBE and LSDA, and 0.80 eV from M06-HF. The ωB97-methods are also found to be accurate for many other optoelectronic properties such as the energy of frontier orbitals and the HOMO-LUMO gap. Our results indicate that the ωB97-method has the potential of predicting the exciton binding energy for more complex systems. From previous work, our results show ωB97 method is possible to estimate the exciton binding energy of molecular organic semiconductors. On the other hand, Pabitra K. Nayak implies B3LYP is possible to estimate the exciton binding energy of molecular organic semiconductors. We compared adiabatic ionization potential, adiabatic electron affinity and vertical optical gap from ωB97 and B3LYP methods to experimental values for 19 molecular organic semiconductors. It verifies ωB97 and B3LYP methods have good prediction for molecular organic semiconductors. Our results indicate that the ωB97 and B3LYP methods have the potential to predict the exciton binding energy for designing new organic optoelectronic materials.
Subjects
exciton binding energy
optical gap
ionization potential
electron affinity
DFT
Type
thesis
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