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seams. One of the seams lies along the nuclear space coordinate that preserves the D3h
point group symmetry (this is the Jahn-Teller seam), and the other one is found in the
subspace where the molecule is distorted from the equilateral triangular geometry to
C2v. There are 3 symmetry-identical MECP of the C2v type.
This interesting feature — 4 very closely located conical intersections — was char-acterized
by Dillon and Yarkony33 and makes the intersection to appear glancing rather
than conical32.
As in the recent study32, we employed EOMEE-CCSD to describe the excited states
of N+3
. As long as the molecule preserves the C2v symmetry, the wavefunctions of
the electronic states of interest belong to different irreps, A2 and B1, and therefore the
derivative coupling matrix element vanishes. The intersection seam between the states
is two-dimensional.
To validate the algorithm, the 21A2/11B1 crossing seams were first scanned in order
to find the minimum energy points. The locations of these points, as well as the points
of triple degeneracy, are listed in Table 5.1.
To assess the performance of the algorithm, we attempted various geometries as the
starting points for the optimization procedure. Usually the algorithm locates the mini-mum
energy points on the 21A2/11B1 seams in less than 20 iterations (Table 5.2). Just
like the local minimum on a global PES found with an optimization algorithm depends
on the starting point, the seam located with the projected gradient method depends on
the choice of the initial molecular geometry.
Another interesting feature of the manifold of the electronic states in N+3
is addi-tional
accidental degeneracies. The 11A2 and 21A2 are degenerate at a point in the
internal coordinate space which happens to correspond to the molecule having the D3h
point group symmetry. Since 21A2 and 11B1 are rigorously degenerate in D3h, the point
144
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 154 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | seams. One of the seams lies along the nuclear space coordinate that preserves the D3h point group symmetry (this is the Jahn-Teller seam), and the other one is found in the subspace where the molecule is distorted from the equilateral triangular geometry to C2v. There are 3 symmetry-identical MECP of the C2v type. This interesting feature — 4 very closely located conical intersections — was char-acterized by Dillon and Yarkony33 and makes the intersection to appear glancing rather than conical32. As in the recent study32, we employed EOMEE-CCSD to describe the excited states of N+3 . As long as the molecule preserves the C2v symmetry, the wavefunctions of the electronic states of interest belong to different irreps, A2 and B1, and therefore the derivative coupling matrix element vanishes. The intersection seam between the states is two-dimensional. To validate the algorithm, the 21A2/11B1 crossing seams were first scanned in order to find the minimum energy points. The locations of these points, as well as the points of triple degeneracy, are listed in Table 5.1. To assess the performance of the algorithm, we attempted various geometries as the starting points for the optimization procedure. Usually the algorithm locates the mini-mum energy points on the 21A2/11B1 seams in less than 20 iterations (Table 5.2). Just like the local minimum on a global PES found with an optimization algorithm depends on the starting point, the seam located with the projected gradient method depends on the choice of the initial molecular geometry. Another interesting feature of the manifold of the electronic states in N+3 is addi-tional accidental degeneracies. The 11A2 and 21A2 are degenerate at a point in the internal coordinate space which happens to correspond to the molecule having the D3h point group symmetry. Since 21A2 and 11B1 are rigorously degenerate in D3h, the point 144 |
