Page 131 |
Save page Remove page | Previous | 131 of 200 | Next |
|
small (250x250 max)
medium (500x500 max)
Large (1000x1000 max)
Extra Large
large ( > 500x500)
Full Resolution
All (PDF)
|
This page
All
|
The observed tendency of triples to lower EOM-CCSD excitation energies is con-sistent
with recent studies27, 28.
4.3.4 MRCI results
The results of MRCI calculations are presented in Table 4.6. Due to its high com-putational
requirements, MRCI2 was only used for the first two singlet excited states.
As reported previously15, the MRCI2 expansion, which includes more correlation than
MRCI1, does not change the excitation energies dramatically. That indicates that the
s–p correlation plays a more important role than double excitations from the active
space.
The MRCI expansions used in these calculations cannot describe Rydberg states
since there are no Rydberg orbitals included in the active space. So even when the basis
set has diffuse functions, the Rydberg states will be too high in energy, and that is why
the second A00 state in the MRCI results is always np , even though in the coupled cluster
calculations Rydberg states appear below the second np .
With the 6-31G(d,p) basis set, the MRCI2 excitations are 5.16 eV and 5.89 eV for
the first two singlet states compared to 5.30 eV and 5.93 eV at the EOM-CCSD/6-
31G(d) level. Thus the MRCI2 energies are blue-shifted by 0.14 eV and 0.04 eV for
the two states compared to EOM-CCSD.With the 6-311+G(d)/6-31G(d,p) basis set, the
MRCI2 energies become 4.87 eV and 5.70 eV. The corresponding excitation energies
using EOM-CCSD and the same basis set [6-311+G(d)/6-31G(d,p)] are 5.22 eV and
5.70 eV. The two methods agree well on the pp energy, but the disagreement for np
has now increased to 0.35 eV. This is mainly because the MRCI2 energy of the lowest
singlet shows a surprisingly large effect on the basis set. With the aug-ANO-DZ basis
set the energy of pp is 5.65 eV, which is very similar to the EOM-CCSD value of
121
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 131 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | The observed tendency of triples to lower EOM-CCSD excitation energies is con-sistent with recent studies27, 28. 4.3.4 MRCI results The results of MRCI calculations are presented in Table 4.6. Due to its high com-putational requirements, MRCI2 was only used for the first two singlet excited states. As reported previously15, the MRCI2 expansion, which includes more correlation than MRCI1, does not change the excitation energies dramatically. That indicates that the s–p correlation plays a more important role than double excitations from the active space. The MRCI expansions used in these calculations cannot describe Rydberg states since there are no Rydberg orbitals included in the active space. So even when the basis set has diffuse functions, the Rydberg states will be too high in energy, and that is why the second A00 state in the MRCI results is always np , even though in the coupled cluster calculations Rydberg states appear below the second np . With the 6-31G(d,p) basis set, the MRCI2 excitations are 5.16 eV and 5.89 eV for the first two singlet states compared to 5.30 eV and 5.93 eV at the EOM-CCSD/6- 31G(d) level. Thus the MRCI2 energies are blue-shifted by 0.14 eV and 0.04 eV for the two states compared to EOM-CCSD.With the 6-311+G(d)/6-31G(d,p) basis set, the MRCI2 energies become 4.87 eV and 5.70 eV. The corresponding excitation energies using EOM-CCSD and the same basis set [6-311+G(d)/6-31G(d,p)] are 5.22 eV and 5.70 eV. The two methods agree well on the pp energy, but the disagreement for np has now increased to 0.35 eV. This is mainly because the MRCI2 energy of the lowest singlet shows a surprisingly large effect on the basis set. With the aug-ANO-DZ basis set the energy of pp is 5.65 eV, which is very similar to the EOM-CCSD value of 121 |
