Computational Chemistry Commons^™

The Investigation Of Singlet Fission From The Perspective Of Hierarchy Of Pure States (Hops), Tao (James) Chen

Chemistry Theses and Dissertations

This thesis provides a preliminary investigation of singlet fission from the perspective of Hierarchy of pure states (HOPS), which provides a numerical exact solution for the investigation of a series of open quantum systems. Since the inception of the concept of singlet fission about half a century ago, this photo-physical process has attracted the attention of a multitude of researchers and has been extensively studied theoretically and experimentally. However, these previous methods for the investigation of singlet fission focus more or less on tackling the underlying mechanisms of singlet fission from the perspective of perturbation. So far, the HOPS method …

C···O And Si···O Tetrel Bonds: Substituent Effects And Transfer Of The Sif3 Group, Zhihao Niu, Qiaozhuo Wu, Qingzhong Li, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The tetrel bond (TB) between 1,2-benzisothiazol-3-one-2-TF₃-1,1-dioxide (T = C, Si) and the O atom of pyridine-1-oxide (PO) and its derivatives (PO-X, X = H, NO₂, CN, F, CH₃, OH, OCH₃, NH₂, and Li) is examined by quantum chemical means. The Si···O TB is quite strong, with interaction energies approaching a maximum of nearly 70 kcal/mol, while the C···O TB is an order of magnitude weaker, with interaction energies between 2.0 and 2.6 kcal/mol. An electron-withdrawing substituent on the Lewis base weakens this TB, while an electron-donating group has the opposite …

Enhanced Quantum Chemistry With Machine Learning, Brock Dyer

Physics and Astronomy Summer Fellows

This file is a catalogue of the relevant quantum mechanical and computer programming topics that I learned during the summer which will be helping me to generate an artificial intelligence that will be able to perform computational chemical calculations at a much faster rate and comparable or better accuracy than current methods.

Modeling Exciton Migration In Two-Dimensional Space, Christian D. Etnyre

DePaul Discoveries

Computational analysis through density matrix quantum mechanics was performed to model exciton migration in two-dimensional space for a zinc-substituted tetraazaphthalocyanine. The model produced resembles a two-dimensional sheet of molecules. Energy transport mechanisms, controlled by point dipole couplings, were evaluated while altering the size of the crystal lattice. It was determined that energy transport was much more significant with a decreasing size of the crystal lattice. Likewise, the result of increasing the size of the crystal lattice had the effect of dampening the rate of energy transport. It was of interest to determine, with varying crystal lattice dimensions, the time that …

N–((2–Acetylphenyl)Carbamothioyl)Benzamide: Synthesis, Crystal Structure Analysis, And Theoretical Studies, Akin Oztaslar, Hakan Arslan

Karbala International Journal of Modern Science

N–((2–Acetylphenyl)carbamothioyl)benzamide has been synthesized and characterized. The molecular conformation of the investigated compound is stabilized by C16–H16B⋅⋅⋅O2ⁱ (i: 1+x, y, z) intermolecular and C14–H14⋅⋅⋅S1, N2–H2⋅⋅⋅O2, and N2–H2⋅⋅⋅O1 intramolecular H–bonds. All DFT calculations have been implemented at the B3LYP level with the 6–311G(d,p) basis set. The optimized molecular structure parameters have been compared with the experimental one in the solid phase. The energy gap, global chemical reactivity descriptor parameters, MEP, Fukui functions, DoS, NLO, and NBO analysis were also computed and investigated. The intermolecular interactions and their energies are evaluated using Hirshfeld surface and energy framework analyses. To determine …

Simulations Of Intruder-Free X-Ray Transient Absorption And Time-Resolved X-Ray Scattering For Probing Attosecond Electron Dynamics, Mengqi Yang

LSU Doctoral Dissertations

The motion of electrons plays a fundamental role in both physics and chemistry, and capturing such dynamics requires the ability to resolve changes at the attosecond timescale, which is enabled by the advent of ultrashort laser pulses. This dissertation aims to facilitate the interpretation of ultrafast electron dynamics and attosecond spectroscopy by real-time time-dependent density functional theory (RT-TDDFT) simulations. The first part of this dissertation focuses on improving the simulation of X-ray transient absorption spectra (XTAS) with Gaussian basis sets in RT-TDDFT by applying a filter to the transition dipole matrix. Due to the spatial limitation of atom-centered Gaussian functions, …

New Methods For Core-Hole Spectroscopy Based On Coupled Cluster Theory, Megan Simons

Chemistry Theses and Dissertations

X-ray absorption spectra (XAS) is a method used to investigate atomic local structure and electronic states. Coupled cluster method is a numerical method used for describing many-body systems and electron correlation in a wavefunction. When equation-of-motion coupled cluster is used in XAS calculations, the ground state is applied to the excitation operator, which excites or ionizes the electron. This causes a large orbital relaxation error, normally ~5 eV, which leads to the need for triple excitations in order to obtain accurate results.

This dissertation introduces a coupled cluster method that uses "transition potential" reference orbitals to reduce the orbital relaxation …

Isolating The Electronic Effects Of Systematic Twist In Highly Substituted Aromatic Hydrocarbons Using Density Functional Theory, Grace Tully, Emily A. Jarvis

Honors Thesis

Density functional theory (DFT) was employed to investigate dodecaphenyltetracene as well as similar molecules containing differing backbone lengths and electron withdrawing groups with interest in manipulating the twist to lower the LUMO level for increased electron mobility. Optimization and frequency time-independent calculations followed by time-dependent (TD-DFT) energy calculations were performed at the B3LYP/G-311G level of theory to analyze electronic trends as a result of increased backbone length and consequently distorted end-to-end molecular twist. These calculations demonstrate a linear relationship with negative slope between the estimated HOMO-LUMO, fundamental, and optical gaps as a function of the number of fused rings along …

Quantum Mechanical Studies Of Water Splitting Reaction With (Zno)3 Nanoclusters As Catalysts, Duwage C. Perera

Electronic Theses and Dissertations

With the current energy crisis, H₂ production through the water-splitting reaction has drawn attention recently. In this thesis, I studied the structural (geometry) and electronic properties (vertical detachment energy and electron affinity) of ZnO monomers and dimers using density functional theory. ZnO is a metal oxide with a 3.37 eV band gap and can be a commercially cheaper photocatalyst in hydrogen (H₂) production. The B3LYP/DGDZVP2 pair was selected after investigating different pairs of exchange functionals and basis sets to study the hydration, hydrolysis, and water-splitting reaction. The singlet-triplet energy gaps of small (ZnO)_n clusters (n=1-6) of …

Developing And Applying Computational Methods On Biomolecules, Shengjie Sun

Open Access Theses & Dissertations

Computational biophysics is an interdisciplinary subject that uses numerical algorithms to study the physical principles underlying biological phenomena and processes. Electrostatic interactions play an important role in computational molecular biophysics and their potential impact on disease mechanisms. At distances larger than several Angstroms, electrostatic interactions dominate all other forces, while the alteration of short-range electrostatic pairwise interactions can also have significant effects. The dual nature of electrostatic interactions, being dominant at long-range and specific at short-range, underscores their profound implications for wild-type structure and function. Any disruption of the complex electrostatic network of interactions may abolish wild-type functionality and could …

Development And Study Of Small Database For The Activation Of Nitrous Oxide Towards Formation Of Iron(Iv)-Oxo Species, Tobias Barthalomew Robertson

Masters Theses

Nitrous oxide (N₂O) can undergo an oxygen atom transfer (OAT) reaction resulting in inert nitrogen gas (N₂O) while transferring an oxygen atom to a molecular complex or material. This process is of catalytic importance since this OAT reaction can be leveraged to form iron(IV)-oxo sites, which are known to be catalytic intermediates. Here, an investigation of the ligand field effects on primarily iron(II) complexes for the formation of iron(IV)-oxo sites with nitrous oxide as the oxidant is reported. An initial database of sixty-four molecular complexes with ligand environments varying in field strength and coordination geometry was …

Development Of Nonorthogonal Wavefunction Theories And Application To Multistate Reaction Processes., Emily Kempfer

Electronic Theses and Dissertations

Many prominent areas of technological development rely on exploiting the photochemical response of molecules. An application of particular interest is the control of molecular switches through a combination of different external stimuli. However, despite significant advances in theoretical approaches and numerous cases of successful application of theory, simulating photochemical reactions remains a computational challenge. Theoretical methods for describing excited states can be broadly divided into single-reference response methods and multireference methods. Single reference methods provide reliable semiquantitative results for single excitations. However, these methods cannot describe double-excited states, systems with strongly correlated ground states, or regions of degeneracy on the …

Probing The Effect Of Nitrogen And Boron Doping On Structures, Properties, And Stability Of C20 Clusters, Ramsay Revennaugh, Martina Kaledin

Symposium of Student Scholars

Fullerenes are carbon molecules arranged in a closed hollow shell to form spherical-like structures. These clusters exist in various sizes, C_n, with the smallest being C₂₀. C₂₀, often when doped with other elements, has shown promise in creating new materials as a catalyst and as energy storage material. Here, we look at the existence of C₂₀ doped with nitrogen or boron atoms using density functional theory (DFT). C₂₀ is doped with one to three boron or nitrogen atoms, respectively, including the five different C₁₈N₂ / C₁₈B_{2 …}

Ab Initio Calculations Of Vibrational Spectra Of Model Peptides, Katheryn Foust, Martina Kaledin

Symposium of Student Scholars

The function of biological molecules is closely related to their spatial structure and conformational dynamics. Therefore, understanding the structure and functions of small peptides contributes to gaining insight into the behavior of more complex systems. The peptide bond (-CO-NH-) is among the very important binding patterns in biochemistry. It links amino acids together, specifies rigidity to the protein backbone, and includes the two essential docking sites for hydrogen-bond-mediated protein folding and protein aggregation, namely, the C=O acceptor and the N-H donor parts. Therefore, the C=O (amide-I) and N-H (amide-A) vibrations provide sensitive and widely used probes into the structure of …

A Comparative Study Of Specific Enthalpy Of Aromatic Hydrocarbons With Simple Carbohydrates, Kohl D. Kervin, Subha Pratihar

ATU Research Symposium

Calorimetry is an aspect of chemistry primarily focused on determining the enthalpy of reactions (∆Hrxn). In the bomb calorimetry technique, the heat of combustion of chemical compounds can be measured experimentally. From this data and the application of Hess’s Law, ∆the Hrxn of several chemical reactions can be determined. The technique of bomb calorimetry can be applied to food, fuels, pharmaceuticals, and many other fields. The objective of the present project is to determine the specific enthalpy of various simple carbohydrates (naturally occurring sugars) through bomb calorimetry and compare it with that of aromatic hydrocarbons.

By performing benzoic acid standardization …

Additivity Of Diene Substituent Gibbs Free Energy Contributions For Diels–Alder Reactions Between Me2c=Cme2 And Substituted Cyclopentadienes, Thomas M. Gilbert, Austin S. Flemming, Brendan C. Dutmer

Faculty Peer-Reviewed Publications

Systematic computational studies of pericyclic Diels–Alder reactions between (H3C)2C═C(CH3)2, 1, and all permutations of substituted cyclopentadienes c-C5R1R2R3R4R5aR5b (R = H, CH3, CF3, F) allowed isolation of substitutional effects on Gibbs free energy barrier heights and reaction Gibbs free energies. “Average Substitution Gibbs Free Energy Correction” ΔGASC#‡/ΔGASC# values for each substituent in each position appeared to be additive. Substituent effects on barriers showed interesting contrasts. Methyl substitution at positions 5a and 5b increased barriers significantly, while substitution at all other positions had essentially no impact. In contrast, fluoro substitution at positions 5a and 5b lowered barriers more than substitution at other …

Exploring Protein Conformations And Functions Through Molecular Dynamics Simulations And Machine Learning, Hao Tian

Chemistry Theses and Dissertations

Proteins are essential biomacromolecules that perform a variety of critical functions in living organisms. The tertiary structure of a protein plays a crucial role in its biological activity as it determines how the protein interacts with other molecules. Consequently, understanding protein conformation and function is an important area of research with implications in medicine, biotechnology, and other fields.

The first part of this dissertation focuses on protein allostery, a process by which proteins transmit perturbations caused by binding at one site to a distal site, thereby regulating activity. With the development of computational methods like molecular dynamics simulations and machine …

Modeling Excited State Processes In Molecular Aggregates By Constructing An Adaptive Basis For The Hierarchy Of Pure States, Leonel Varvelo

Chemistry Theses and Dissertations

Simulating excitation energy transfer (EET) in molecular materials is of crucial importance for the development of and understanding of materials such as organic photovoltaics and photosynthetic systems and further development of novel materials. The Hierarchy of Pure States (HOPS) is an exact framework for the time evolution of an open quantum system in which a hierarchy of stochastic wave functions are propagated in time. The adaptive HOPS (adHOPS) method achieves size-invariant scaling with the number of simulated molecules for sufficiently large aggregates by using an adaptive basis that moves with the excitation through the material. To demonstrate the power of …

Chatgpt As Metamorphosis Designer For The Future Of Artificial Intelligence (Ai): A Conceptual Investigation, Amarjit Kumar Singh (Library Assistant), Dr. Pankaj Mathur (Deputy Librarian)

Library Philosophy and Practice (e-journal)

Abstract

Purpose: The purpose of this research paper is to explore ChatGPT’s potential as an innovative designer tool for the future development of artificial intelligence. Specifically, this conceptual investigation aims to analyze ChatGPT’s capabilities as a tool for designing and developing near about human intelligent systems for futuristic used and developed in the field of Artificial Intelligence (AI). Also with the helps of this paper, researchers are analyzed the strengths and weaknesses of ChatGPT as a tool, and identify possible areas for improvement in its development and implementation. This investigation focused on the various features and functions of ChatGPT that …

Minimal Auxiliary Basis Set Approach For The Electronic Excitation Spectra Of Organic Molecules, Zehao Zhou, Shane M. Parker

Faculty Scholarship

We report a minimal auxiliary basis model for time-dependent density functional theory (TDDFT) with hybrid density functionals that can accurately reproduce excitation energies and absorption spectra from TDDFT while reducing cost by about \change{two} orders of magnitude. Our method, dubbed TDDFT-ris, employs the resolution-of-the-identity technique with just one $s$-type auxiliary basis function per atom for the linear response operator, where the Gaussian exponents are parametrized across the periodic table using %using tabulated atomic radii with a single global scaling factor. By tuning on a small test set, we determine a single functional-independent scale factor that balances errors in excitation energies …