Why Does the Optimal Tuning Method of the Range Separation Parameter of a Long-Range Corrected Density Functional Fail in Intramolecular Charge Transfer Excitation Calculations?
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引用次数: 0
Abstract
We performed intra- and intermolecular charge transfer (CT) excitation energy calculations of (a) conjugated carbon chain [H2N–(CH=CH)n–X] and (b) its equidistant H2NH∙∙∙HX (n = 2~8) with various electron acceptors (X = NH2, OH, Cl, CHO, CN, and NO2) using EOM-CCSD, time-dependent (TD) Hartree–Fock (HF) and various density functional theory (DFT) functionals, such as BLYP, B3LYP, long-range corrected (LC) DFT, and LC-DFT with an optimally tuned (OT) range separation parameter (µ) using Koopman’s theorem to investigate the effect of the electron-withdrawing (or -donating) strength of end-capped functional group (X) and CT distance (R) on intra- and intermolecular CT excitation energies. As the electron-withdrawing strength of X increases, both intra- and intermolecular CT excitation energies tend to decrease, since energy gaps between orbitals corresponding to CT excitations (e.g., HOMO and LUMO) decrease. However, the effect of the electron-withdrawing group on intramolecular CT excitation energy is negligible (at most 0.5 eV). OT-LC-DFT shows accurate intermolecular CT excitation energy, but worse results in intramolecular CT excitation energy than LC-DFT with the default µ value (0.47). Therefore, we conclude that the optimal tuning method is not effective in predicting intramolecular CT excitation energy. While intermolecular CT excitation energy has excitonic binding energy with asymptotic behavior to CT distance that is not affected by the choice of range separation parameter, intramolecular CT excitation energy is affected by orbital relaxation energy, which strongly depends on the choice of range separation parameter, which makes the OT method of range separation parameter ineffective in predicting intramolecular CT excitation energy as well as local excitation with high accuracy.
期刊介绍:
Molecules (ISSN 1420-3049, CODEN: MOLEFW) is an open access journal of synthetic organic chemistry and natural product chemistry. All articles are peer-reviewed and published continously upon acceptance. Molecules is published by MDPI, Basel, Switzerland. Our aim is to encourage chemists to publish as much as possible their experimental detail, particularly synthetic procedures and characterization information. There is no restriction on the length of the experimental section. In addition, availability of compound samples is published and considered as important information. Authors are encouraged to register or deposit their chemical samples through the non-profit international organization Molecular Diversity Preservation International (MDPI). Molecules has been launched in 1996 to preserve and exploit molecular diversity of both, chemical information and chemical substances.