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ionization continuum in CIS/TDDFT calculations. Thus, with B3LYP, the continuum
begins 1.54 eV below its own VDE, whereas the situation with wPB97X is reverse —
the continuum states appear 0.44 eV above the respective VDE. BNL, by constriction,
is internally consistent, and the continuum states in TDDFT calculations appear exactly
at the respective VDE.
Thus, our estimate of VDE is 2.4–2.5 eV, within 0.1 eV from the maximum of the
weak absorption feature at 2.3 eV. The remaining discrepancy between the two values
might be due to the uncertainties in equilibrium geometries or possibl vibrational exci-tation
of the molecules in the experiment.
Although correlation has significant effect on VDE, the ionized state has Koopmans-like
character, i.e. the leading EOM-IP amplitude corresponds to ionization from the
HOMO (see Fig. 2.3) and equals 0.96. Thus the Hartree–Fock HOMO is a good approx-imation
to a correlated Dyson orbital33.
2.3.3 Vertical excitation energy and electronic properties of the sin-glet
and triplet pp transitions of the HBDI anion
Singlet pp state: Benchmark results
Motivated by the discrepancies in previous theoretical estimates of the pp excitation
energy of the HBDI anion (Table 1.1), we set out to benchmark other electronic struc-ture
methods, with the purpose of identifying a rigorous yet fairly inexpensive quantum
chemistry approach that can be employed in condensed-phase applications. The experi-mental
maximum of absorption is at 2.59 eV (479 nm), and the band’s full width at half
maximum (FWHM) is 0.25 eV (45 nm)28, 29. Assuming that the absorption maximum
corresponds to the vertical transition of the lowest-energy isomer (which is not entirely
50
Object Description
| Title | Development of predictive electronic structure methods and their application to atmospheric chemistry, combustion, and biologically relevant systems |
| Author | Epifanovskiy, Evgeny |
| Author email | epifanov@usc.edu; epifanov@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemistry |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2011-03-21 |
| Date submitted | 2011 |
| Restricted until | Unrestricted |
| Date published | 2011-04-28 |
| Advisor (committee chair) | Krylov, Anna I. |
| Advisor (committee member) |
Wittig, Curt Johnson, Clifford |
| Abstract | This work demonstrates electronic structure techniques that enable predictive modeling of the properties of biologically relevant species. Chapters 2 and 3 present studies of the electronically excited and detached states of the chromophore of the green fluorescent protein, the mechanism of its cis-trans isomerization, and the effect of oxidation. The bright excited ππ∗ state of the chromophore in the gas phase located at 2.6 eV is found to have an autoionizing resonance nature as it lies above the electron detachment level at 2.4 eV. The calculation of the barrier for the ground-state cis-trans isomerization of the chromophore yields 14.8 kcal/mol, which agrees with an experimental value of 15.4 kcal/mol; the electronic correlation and solvent stabilization are shown to have an important effect. In Chapter 3, a one-photon two-electron mechanism is proposed to explain the experimentally observed oxidative reddening of the chromophore. Chapter 4 considers the excited states of uracil. It demonstrates the role of the one-electron basis set and triples excitations in obtaining the converged values of the excitation energies of the nπ∗ and ππ∗ states. The effects of the solvent and protein environment are included in some of the models.; Chapter 5 describes an implementation of the algorithm for locating and exploring intersection seams between potential energy surfaces. The theory is illustrated with examples from atmospheric and combustion chemistry. |
| Keyword | electronic structure theory; coupled clusters theory; equation of motion theory; organic chromophore; green fluorescent protein; uracil |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3801 |
| Contributing entity | University of Southern California |
| Rights | Epifanovskiy, Evgeny |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Epifanovskiy-4557 |
| Archival file | uscthesesreloadpub_Volume14/etd-Epifanovskiy-4557.pdf |
Description
| Title | Page 60 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | ionization continuum in CIS/TDDFT calculations. Thus, with B3LYP, the continuum begins 1.54 eV below its own VDE, whereas the situation with wPB97X is reverse — the continuum states appear 0.44 eV above the respective VDE. BNL, by constriction, is internally consistent, and the continuum states in TDDFT calculations appear exactly at the respective VDE. Thus, our estimate of VDE is 2.4–2.5 eV, within 0.1 eV from the maximum of the weak absorption feature at 2.3 eV. The remaining discrepancy between the two values might be due to the uncertainties in equilibrium geometries or possibl vibrational exci-tation of the molecules in the experiment. Although correlation has significant effect on VDE, the ionized state has Koopmans-like character, i.e. the leading EOM-IP amplitude corresponds to ionization from the HOMO (see Fig. 2.3) and equals 0.96. Thus the Hartree–Fock HOMO is a good approx-imation to a correlated Dyson orbital33. 2.3.3 Vertical excitation energy and electronic properties of the sin-glet and triplet pp transitions of the HBDI anion Singlet pp state: Benchmark results Motivated by the discrepancies in previous theoretical estimates of the pp excitation energy of the HBDI anion (Table 1.1), we set out to benchmark other electronic struc-ture methods, with the purpose of identifying a rigorous yet fairly inexpensive quantum chemistry approach that can be employed in condensed-phase applications. The experi-mental maximum of absorption is at 2.59 eV (479 nm), and the band’s full width at half maximum (FWHM) is 0.25 eV (45 nm)28, 29. Assuming that the absorption maximum corresponds to the vertical transition of the lowest-energy isomer (which is not entirely 50 |
