Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 9 of 9

Full-Text Articles in Physics

Conformational Dependence Of Σ-Electron Delocalization In The Catenae Xnme2n+2, X = Si, Ge, Sn, And Pb, Milena Jovanovic Jan 2019

Conformational Dependence Of Σ-Electron Delocalization In The Catenae Xnme2n+2, X = Si, Ge, Sn, And Pb, Milena Jovanovic

Chemistry Graduate Theses & Dissertations

Bonds of σ type are the most common chemical bonds, dominating bonding in all molecules and defining the framework of a molecule. It has been long known that electrons in σ bonds can delocalize throughout a molecule. However, the nature of σ-electron delocalization is not fully understood due to its complexity. One of the important aspects of σ-electron delocalization is its conformational dependence, first noted in oligosilanes where properties of a molecule change drastically when it changes conformation. This dissertation describes efforts to understand the conformational dependence of σ delocalization in oligosilanes and their heavier analogs using simple intuitive models ...


The Role Of Defects On The Optical, Electronic, And Magnetic Properties Of Iron-Sulfur Solids, Alyssa Ruth Landin Jan 2018

The Role Of Defects On The Optical, Electronic, And Magnetic Properties Of Iron-Sulfur Solids, Alyssa Ruth Landin

Chemistry & Biochemistry Graduate Theses & Dissertations (1986-2018)

Solids composed of iron and sulfur are earth abundant and nontoxic, and can exhibit interesting and technologically important optical, electronic, and magnetic phenomena. Troilite (hexagonal FeS) is predicted to exhibit large room temperature magnetoelectricity and may exhibit high temperature superconducting properties, and pyrite (cubic FeS2) is a promising candidate for photovoltaic

applications. However, defects naturally occur within both of these solids. Troilite contains Fe deficiencies with atomic formula Fe(1-x)S, while pyrite contains sulfur deficiencies with the atomic formula FeS(2-x). The Fe-S phase diagram is congested in these regions of slight non-stoichiometries, and even when the atomic ...


Investigating The Properties Of Superfluid He-4 Through Density Functional Calculations, Matthew Francis Dutra May 2017

Investigating The Properties Of Superfluid He-4 Through Density Functional Calculations, Matthew Francis Dutra

Doctoral Dissertations

We present a study of isotopically pure He-4 systems evaluated using helium density functional theory (He-DFT) with the intent of better understanding their ground state structural and energetic properties, particularly within the scope of singularly-doped helium droplets. We self-consistently solve for the density profiles and chemical potentials for a wide range of pure helium droplet sizes (up to 9500 atoms) via an imaginary time propagation method, and fit the resultant energetic data to a power law formula to be able to extrapolate values for even larger droplets. Subsequent calculations on singularly-doped droplets within the same size range yield accurate binding ...


Growth And Characterization Of Baznga, Na Hyun Jo, Qisheng Lin, Udhara S. Kaluarachchi, William R. Meier, Soham Manni, Savannah S. Downing, Anna E. Böhmer, Tai Kong, Yang Sun, Valentin Taufour, Cai-Zhuang Wang, Kai-Ming Ho, Sergey L. Bud’Ko, Paul C. Canfield Jan 2017

Growth And Characterization Of Baznga, Na Hyun Jo, Qisheng Lin, Udhara S. Kaluarachchi, William R. Meier, Soham Manni, Savannah S. Downing, Anna E. Böhmer, Tai Kong, Yang Sun, Valentin Taufour, Cai-Zhuang Wang, Kai-Ming Ho, Sergey L. Bud’Ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report the growth, structure and characterization of BaZnGa, identifying it as the sole known ternary compound in the Ba–Zn–Ga system. Single crystals of BaZnGa can be grown out of excess Ba–Zn and adopt a tI36 structure type. There are three unique Ba sites and three M = Zn/Ga sites. Using DFT calculations we can argue that whereas one of these three M sites is probably solely occupied by Ga, the other two M sites, most likely, have mixed Zn/Ga occupancy. Temperature-dependent resistivity and magnetization measurements suggest that BaZnGa is a poor metal with no electronic ...


Comparison Of S-Adsorption On (111) And (100) Facets Of Cu Nanoclusters, Jeffrey S. Boschen, Jiyoung Lee, Theresa L. Windus, James W. Evans, Patricia A. Thiel, Da-Jiang Liu Oct 2016

Comparison Of S-Adsorption On (111) And (100) Facets Of Cu Nanoclusters, Jeffrey S. Boschen, Jiyoung Lee, Theresa L. Windus, James W. Evans, Patricia A. Thiel, Da-Jiang Liu

Physics and Astronomy Publications

In order to gain insight into the nature of chemical bonding of sulfur atoms on coinage metal surfaces, we compare the adsorption energy and structural parameters for sulfur at four-fold hollow (4fh) sites on (100) facets and at three-fold hollow (3fh) sites on (111) facets of Cu nanoclusters. Consistent results are obtained from localized atomic orbital and plane-wave based density functional theory using the same functionals. PBE and its hybrid counterpart (PBE0 or HSE06) also give similar results. 4fh sites are preferred over 3fh sites with stronger bonding by ∼0.6 eV for nanocluster sizes above ∼280 atoms. However, for ...


Fractional Charge Methods For Correcting Approximate Kohn-Sham Potentials, Darya N. Komsa Aug 2016

Fractional Charge Methods For Correcting Approximate Kohn-Sham Potentials, Darya N. Komsa

Electronic Thesis and Dissertation Repository

The Kohn-Sham density functional theory relies on approximating the exchange-correlation energy functional or the corresponding potential. The behavior of the exchange-correlation potential as a function of position in a system can be used to detect and correct deficiencies of the parent functional. The too-fast decay of the potentials derived from common density functionals is a major problem, because it causes inaccurate Rydberg excitation energies and erroneous fractional charges in dissociating molecules. An efficient method to correct the shape of the exchange-correlation potential was proposed by Gaiduk et al. [A. P. Gaiduk, D. S. Firaha, and V. N. Staroverov, Phys. Rev ...


Theory Of Model Kohn-Sham Potentials And Its Applications, Alex P. Gaiduk Jan 2013

Theory Of Model Kohn-Sham Potentials And Its Applications, Alex P. Gaiduk

Electronic Thesis and Dissertation Repository

The purpose of Kohn-Sham density functional theory is to develop increasingly accurate approximations to the exchange-correlation functional or to the corresponding potential. When one chooses to approximate the potential, the resulting model must be integrable, that is, a functional derivative of some density functional. Non-integrable potentials produce unphysical results such as energies that are not translationally or rotationally invariant. The thesis introduces methods for constructing integrable model potentials, developing properly invariant energy functionals from model potentials, and designing model potentials that yield accurate electronic excitation energies. Integrable potentials can be constructed using powerful analytic integrability conditions derived in this work ...


Organic Photovoltaics: A Charge Transfer Perspective In The Study Of Donor-Acceptor Systems, Marco Olguin Jan 2013

Organic Photovoltaics: A Charge Transfer Perspective In The Study Of Donor-Acceptor Systems, Marco Olguin

Open Access Theses & Dissertations

The present research involves the study of donor-acceptor (D/A) dyad complexes from a charge transfer energy perspective. The aim is to provide insight and predictive understanding into the charge transfer processes of the molecular-level components in donor-acceptor based organic solar cells using computational methods to describe photochemical processes at the quantum mechanical level within the Density Functional Theory (DFT) approximation. Predictive understanding is anchored in reproducing experimental results, wherein the present work a perturbative excited-state DFT method is described in detail and shown to give Charge Transfer (CT) energies in excellent agreement with benchmark experimental data. With an accurate ...


Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel Jan 2010

Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

H2S forms a rich variety of structures on Ag(111) at low temperature and submonolayer coverage. The molecules decorate step edges, exist as isolated entities on terraces, and aggregate into clusters and islands, under various conditions. One type of island exhibits a (×)R25.3° unit cell. Typically, molecules in the clusters and islands are separated by about 0.4 nm, the same as the S–S separation in crystalline H2S. Density functional theory indicates that hydrogen-bonded clusters contain two types of molecules. One is very similar to an isolated adsorbed H2S molecule, with both ...