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states. Increasing the size of the one-electron basis brings the continuum states down.
When the basis set is large enough to accommodate a detached electron, the lowest
excited state will correspond to the detached state (this fact has been exploited in pilot
implementations of EOMIP-CCSD based on the EOMEE-CCSD code by adding a very
diffuse orbital to the basis to describe the ionized electron35, 36). It can be shown for-mally,
that in the case of CIS and TD-DFT, the energy of the lowest of such CIS-IP states
equals the HOMO energy, that is, the Koopmans theorem can be proven by considering
configuration interaction of all singly detached determinants.
When the one-electron basis set is expanded with diffuse functions, the density of
states rapidly increases with both CIS and TD-DFT (BNL), as illustrated in Fig. 2.4. At
the same time, the lowest excited state converges to Koopmans’ VDE. Both methods
split the oscillator strength of the bright pp transition among multiple states, but BNL
does that to a larger degree, which results in three to four states with close oscillator
strengths (Table 2.1). That may be due to the remaining self-interaction error in BNL
calculations.
The lowest excited CIS and TD-DFT states shown in Fig. 2.4 fall below the Koop-mans
estimate in large basis sets due to additional stabilization by the interaction with
other CIS determinants that vanish once the detached electron is infinitely far from
the core. Indeed, if a separate large non-interacting orbital is used instead of diffuse
functions, the lowest excitation energy in such a system is exactly equal to the HOMO
energy.
As the density of low-lying states that approximate the continuum increases and the
oscillator strength gets redistributed, it becomes increasingly more difficult to compute
or even identify the resonance state. By following the evolution of the states with the
basis set increase, the limiting value of the resonance state can be extrapolated using the
52
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 62 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | states. Increasing the size of the one-electron basis brings the continuum states down. When the basis set is large enough to accommodate a detached electron, the lowest excited state will correspond to the detached state (this fact has been exploited in pilot implementations of EOMIP-CCSD based on the EOMEE-CCSD code by adding a very diffuse orbital to the basis to describe the ionized electron35, 36). It can be shown for-mally, that in the case of CIS and TD-DFT, the energy of the lowest of such CIS-IP states equals the HOMO energy, that is, the Koopmans theorem can be proven by considering configuration interaction of all singly detached determinants. When the one-electron basis set is expanded with diffuse functions, the density of states rapidly increases with both CIS and TD-DFT (BNL), as illustrated in Fig. 2.4. At the same time, the lowest excited state converges to Koopmans’ VDE. Both methods split the oscillator strength of the bright pp transition among multiple states, but BNL does that to a larger degree, which results in three to four states with close oscillator strengths (Table 2.1). That may be due to the remaining self-interaction error in BNL calculations. The lowest excited CIS and TD-DFT states shown in Fig. 2.4 fall below the Koop-mans estimate in large basis sets due to additional stabilization by the interaction with other CIS determinants that vanish once the detached electron is infinitely far from the core. Indeed, if a separate large non-interacting orbital is used instead of diffuse functions, the lowest excitation energy in such a system is exactly equal to the HOMO energy. As the density of low-lying states that approximate the continuum increases and the oscillator strength gets redistributed, it becomes increasingly more difficult to compute or even identify the resonance state. By following the evolution of the states with the basis set increase, the limiting value of the resonance state can be extrapolated using the 52 |
