Physics Commons^™

Dynamic Effects In Electron Momentum Spectroscopy Of Sulfur Hexafluoride, Xing Wang, Shenyue Xu, Chuangang Ning, O. Al-Hagan, Pengfei Hu, Yongtao Zhao, Zhongfen Xu, Jingkang Deng, Enliang Wang, Xueguang Ren, Alexander Dorn, Don H. Madison

Physics Faculty Research & Creative Works

Electron momentum spectroscopy (EMS) results are presented for the sulfur hexafluoride (SF6) molecule using a high-resolution binary (e, 2e) spectrometer at incident energies (Ei) of 600, 1200, and 2400 eV plus the binding energy. The valence orbital momentum profiles were measured with a binding energy resolution of 0.68 eV and angular resolutions of Δθ = ±0.6⁰, ΔΦ = ±0.85⁰. Whereas the two higher incident energies are in the range where normally EMS measurements do not exhibit an impact-energy dependence, the current experimental data display a dynamic dependence on the impact energies. The measured momentum profiles are compared with predictions from …

Dissipation Effects In Schrödinger And Quantal Density Functional Theories Of Electrons In An Electromagnetic Field, Xiao-Yin Pan, Viraht Sahni

Publications and Research

Dissipative effects arise in an electronic system when it interacts with a time-dependent environment. Here, the Schrödinger theory of electrons in an electromagnetic field including dissipative effects is described from a new perspective. Dissipation is accounted for via the effective Hamiltonian approach in which the electron mass is time-dependent. The perspective is that of the individual electron: the corresponding equation of motion for the electron or time-dependent differential virial theorem—the ‘Quantal Newtonian’ second law—is derived. According to the law, each electron experiences an external field comprised of a binding electric field, the Lorentz field, and the electromagnetic field. In addition, …

Mc-Pdft Can Calculate Singlet-Triplet Splittings Of Organic Diradicals., Samuel J. Stoneburner, Donald G. Truhlar, Laura Gagliardi

Educator Scholarship

The singlet-triplet splittings of a set of diradical organic molecules are calculated using multiconfiguration pair-density functional theory (MC-PDFT) and the results are compared with those obtained by Kohn-Sham density functional theory (KS-DFT) and complete active space second-order perturbation theory (CASPT2) calculations. We found that MC-PDFT, even with small and systematically defined active spaces, is competitive in accuracy with CASPT2, and it yields results with greater accuracy and precision than Kohn-Sham DFT with the same parent functional. MC-PDFT also avoids the challenges associated with spin contamination in KS-DFT. It is also shown that MC-PDFT is much less computationally expensive than CASPT2 …

Synergistic Interactions Of H2 And N2 With Molten Gallium In The Presence Of Plasma, Maria L. Carreon, Daniel F. Jaramillo-Cabanzo, Indira Chaudhuri, Madhu Menon, Mahendra K. Sunkara

Physics and Astronomy Faculty Publications

The present study examines the interaction of hydrogen and nitrogen plasmas with gallium in an effort to gain insights into the mechanisms behind the synergetic effect of plasma and a catalytic metal. Absorption/desorption experiments were performed, accompanied by theoretical-computational calculations. Experiments were carried out in a plasma-enhanced, Ga-packed, batch reactor and entailed monitoring the change in pressure at different temperatures. The results indicated a rapid adsorption/dissolution of the gas into the molten metal when gallium was exposed to plasma, even at a low temperature of 100 °C. The experimental observations, when hydrogen was used, indicate that gallium acts as a …

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 …

The Effect Of Pressure And Interstitial Substitution On The Electronic Properties Of Molybdenum Disulfide Mos2, Wadha Khalifa Salem Rashed Alfalasi

Physics Theses

Molybdenum disulfide has some of graphene’s properties but has an edge over graphene as this new 2D nanomaterial has a band gap in its electronic structure, which is absent in graphene. The purpose of this thesis is to study the electronic properties of the promising Molybdenum Disulfide (MoS2) material in its bulk and monolayer forms by undertaking a systematic theoretical approach. We will mainly study the band gap, the density of states and the electronic charge distribution, which is considered as the most important electronic characteristics of semiconductors.

In this study, the density functional theory (DFT) – implemented in WIEN2k …

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. …

Defect Driven Magnetism In Doped Sno2 Nanoparticles: Surface Effects, Pushpa Raghani, Pankaj Kumar, Balaji Ramanujam, Alex Punnoose

Physics Faculty Publications and Presentations

Magnetism and energetics of intrinsic and extrinsic defects and defect clusters in bulk and surfaces of SnO₂ is investigated using first-principles to understand the role of surfaces in inducing magnetism in Zn doped nanoparticles. We find that Sn vacancies induce the largest magnetic moment in bulk and on surfaces. However, they have very large formation energies in bulk as well as on surfaces. Oxygen vacancies on the other hand are much easier to create than V_Sn, but neutral and V_O⁺² vacancies do not induce any magnetism in bulk as well as on surfaces. V_{O …}

Defect Driven Magnetism In Doped Sno2 Nanoparticles: Surface Effects, Pushpa Raghani, Pankaj Kumar, Balaji Ramanujam, Alex Punnoose

Pushpa Raghani

Magnetism and energetics of intrinsic and extrinsic defects and defect clusters in bulk and surfaces of SnO2 is investigated using first-principles to understand the role of surfaces in inducing magnetism in Zn doped nanoparticles. We find that Sn vacancies induce the largest magnetic moment in bulk and on surfaces. However, they have very large formation energies in bulk as well as on surfaces. Oxygen vacancies on the other hand are much easier to create than VSn, but neutral and VO+2 vacancies do not induce any magnetism in bulk as well as on surfaces. VO+1 induce small magnetism in bulk and …

The Closo-Si12C12 Molecule From Cluster To Crystal: A Theoretical Prediction, Xiaofeng F. Duan, Larry W. Burggraf

Faculty Publications

The structure of closo-Si₁₂C₁₂ is unique among stable Si_nC_m isomers (n, m > 4) because of its high symmetry, π–π stacking of C₆ rings and unsaturated silicon atoms at symmetrical peripheral positions. Dimerization potential surfaces reveal various dimerization reactions that form between two closo-Si₁₂C₁₂ molecules through Si–Si bonds at unsaturated Si atoms. As a result the closo-Si₁₂C₁₂ molecule is capable of polymerization to form stable 1D polymer chains, 2D crystal layers, and 3D crystals. 2D crystal structures formed by side-side polymerization satisfy eight Si valences on each monomer …

Scalability Improvements To Nrlmol For Dft Calculations Of Large Molecules, Carlos Manuel Diaz

Open Access Theses & Dissertations

Advances in high performance computing (HPC) have provided a way to treat large, computationally demanding tasks using thousands of processors. With the development of more powerful HPC architectures, the need to create efficient and scalable code has grown more important. Electronic structure calculations are valuable in understanding experimental observations and are routinely used for new materials predictions. For the electronic structure calculations, the memory and computation time are proportional to the number of atoms. Memory requirements for these calculations scale as N2, where N is the number of atoms. While the recent advances in HPC offer platforms with large numbers …

A Comparative Study Of The Electronic Properties Of Aluminum Nitride Compounds, Rezek Mohammad, Şenay Katircioğlu

Turkish Journal of Physics

Electronic properties of aluminum nitride in wurtzite, zinc-blende, and rock-salt phases are investigated by a full potential-linearized augmented plane waves method based on density functional theory within standard local density approximation and its four improved versions. Local density approximation corrected by the generalized gradient functional of Perdew-Wang-Engel-Vosko is found to be more successful than the other generalized gradient functional approximations considered in this work for providing reasonable lattice constants, energy gaps, effective electron and hole masses, and optical features for AlN phases. Although local density approximation corrected by modified Becke-Johnson potential underestimates the static dielectric constants, it provides the largest …

First-Principles Studies Of Group Iv And Group V Related Two Dimensional Materials, Gaoxue Wang

Dissertations, Master's Theses and Master's Reports

Two dimensional (2D) materials have been extensively studied due to their novel properties and technologically important applications. Especially, the discovery of graphene has stimulated an avalanche of investigations to exploit its novel properties for applications at nanoscale. In the post-silicon era, graphene has been widely regarded as the most promising building blocks for the electronic devices. However, its metallic nature together with sensitivity to the environment leads to somewhat limited scope of applications. A finite band gap in a material is known to be essential for the fabrication of devices such as transistors. Such a limitation associated with graphene has …

Electronic Structure And Insulating Gap In Epitaxial Vo2 Polymorphs, Shinbuhm Lee, Tricia L. Meyer, Changhee Sohn, Donghwa Lee, John Nichols, Dongkyu Lee, Sung S. Ambrose Seo, John W. Freeland, Tae Won Noh, Ho Nyung Lee

Physics and Astronomy Faculty Publications

Determining the origin of the insulating gap in the monoclinic VO₂(M1) is a long-standing issue. The difficulty of this study arises from the simultaneous occurrence of structural and electronic transitions upon thermal cycling. Here, we compare the electronic structure of the M1 phase with that of single crystalline insulating VO₂(A) and VO₂(B) thin films to better understand the insulating phase of VO₂. As these A and B phases do not undergo a structural transition upon thermal cycling, we comparatively study the origin of the gap opening in the insulating VO₂ phases. …

Electronic Structures Of Lanthanum, Samarium, And Gadolinium Sulfides, Lu Wang, Chris M. Marin, Wai-Ning Mei, Chin Li Cheung

Physics Faculty Publications

In this study, we report our efforts to elucidate the electronic structures of two lattice structures of lanthanide sulfides (LnS and Ln3S4) and for three lanthanides (Ln = La, Sm and Gd) using density functional theory calculations performed with the CASTEP code. A DFT+U method was used for the corrections of on-site Coulomb interactions with U = 6 eV. The calculated electronic structures show that both lanthanum and gadolinium sulfides have metallic properties, consistent with the available experimental results. However, the calculated electronic structure of Sm3S4 is considerably different from those of the La3S4 and Gd3S4 and is predicted to …

Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, Suwit Suthirakun, Salai Ammal, Guoliang Xiao, Fanglin Chen, Kevin Huang, Hans Zur Loye, Andreas Heyden

Salai C. Ammal

No abstract provided.

Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Kevin Huang, Hans-Conrad Zur Loye, Andreas Heyden

Salai C. Ammal

No abstract provided.

Π-Systems As Lithium/Hydrogen Bond Acceptors: Some Theoretical Observations, Salai Ammal, P. Venuvanalingam

Salai C. Ammal

Ab initio calculations at the Hartree–Fock and correlated levels and density functional theory calculations have been performed with 6-31++G(d,p) and 6-311++G(d,p)basis sets on LiF and HF complexes of benzene, ethylene, and acetylene. Complex binding energies have been corrected for basis set superposition error, and zero point energy corrections have been done on Hartree–Fock binding energies. Computed results indicate that the complexes exist in different conformations and among them those with π-lithium and π-hydrogen bonds are the most stable. π-lithium bonds are stronger than π-hydrogen bonds. The computed binding energies and geometry of HF complexes correlate well with the available experimental …

Chemical Interaction Of Nf3 With Si (Part Ii): Density Functional Calculation Studies, A. Endou, T. Little, A. Yamada, K. Teraishi, M. Kubo, Salai Ammal, A. Miyamoto, M. Kitajima, F. Ohuchi

Salai C. Ammal

No abstract provided.

Density Functional Theory Study On The Electronic Structure Of N- And P-Type Doped Srtio3 At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden

Salai C. Ammal

The electronic conductivity and thermodynamic stability of mixed n-type and p-type doped SrTiO3 have been investigated at anodic solid oxide fuel cell (SOFC) conditions using density functional theory (DFT) calculations. In particular, constrained ab initio thermodynamic calculations have been performed to evaluate the phase stability and reducibility of various Nb- and Ga-doped SrTiO3 at synthesized and anodic SOFC conditions. The density of states (DOS) of these materials was analyzed to study the effects of n- and p-doping on the electronic conductivity. In agreement with experimental observations, we find that the transformation from 20% Nb-doped Sr-deficient SrTiO3 to a non-Sr-deficient phase …

Adsorption Of Co2 Molecule On The (Mgo)9 And (Cao)9 Nanoclusters; A Theoretical Study, Innovative Research Publications Irp India, Fathi Hassan Bawa

Innovative Research Publications IRP India

Binding configurations of CO2 on (MgO)9 and (CaO)9 cluster models are investigated by means of density functional theory model calculations. The results show that CO2 adsorbs as monodentate on MgO and CaO terrace site leads to formation of surface carbonates CO3 2- . Marginal differences in the binding stabilities between the CO2 molecule and surface O2- site were found to be significantly similar. The estimated adsorption energies are 1.47 eV and 1.52 eV at the (MgO)9 and (CaO)9 clusters, respectively. The similarity in binding energies is discussed in terms of cluster electropositivity. Adsorbed CO2, to (MgO)9 surface vibration frequencies are …

Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, Suwit Suthirakun, Salai Ammal, Guoliang Xiao, Fanglin Chen, Kevin Huang, Hans Zur Loye, Andreas Heyden

Kevin Huang

No abstract provided.

Using Graphene To Control Magnetic Anisotropy And Interaction Between Supported Clusters, Sanjubala Sahoo, M Fhokrul Islam, Shiv N. Khanna

Physics Publications

Stabilization of magnetic order in clusters/nanoparticles at elevated temperatures is a fundamentally challenging problem. The magnetic anisotropy energy (MAE) that prevents the thermal fluctuations of the magnetization direction can be around 1–10 K in free transition metal clusters of around a dozen atoms. Here we demonstrate that a graphene support can lead to an order of magnitude enhancement in the anisotropy of supported species. Our studies show that the MAE of supported Co5 and Co13 clusters on graphene increase by factors of 2.6 and 25, respectively. The enhancement is linked to the splitting of selected electronic orbitals that leads to …

Rhodizonic Acid On Noble Metals: Surface Reactivity And Coordination Chemistry, Donna A. Kunkel, James Hooper, Scott Simpson, Sumit Beniwal, Katie L. Morrow, Douglas C. Smith, Kimberly Cousins, Stephen Ducharme, Eva Zurek, Axel Enders

Axel Enders

A study of the two-dimensional crystallization of rhodizonic acid on the crystalline surfaces of gold and copper is presented. Rhodizonic acid, a cyclic oxocarbon related to the ferroelectric croconic acid and the antiferroelectric squaric acid, has not been synthesized in bulk crystalline form yet. Capitalizing on surface-assisted molecular self-assembly, a two-dimensional analogue to the well-known solution-based coordination chemistry, two-dimensional structures of rhodizonic acid were stabilized under ultrahigh vacuum on Au(111) and Cu(111) surfaces. Scanning tunneling microscopy, coupled with first-principles calculations, reveals that on the less reactive Au surface, extended two-dimensional islands of rhodizonic acid are formed, in which the molecules …

A Study On Si And P Doped H-Bn Sheets: Dft Calculations, Hati̇ce Kökten, Şaki̇r Erkoç

Turkish Journal of Physics

Structural properties and energetics of silicon and phosphorus doped hexagonal boron nitride sheets were investigated by performing density functional theory calculations. The dopant atoms were substituted in a neutral charge state at either the B or the N site in the system as an impurity. All the systems under consideration were fully optimized. A systematic study was performed to see the effect of cell size on the calculated quantities, such as bond length, charge transfer, and defect formation energies. It was found that both silicon and phosphorus atom substitutions cause the bond lengths to increase with respect to the pristine …

Electronic Structure And Charge Transfer Excited States Of Endohedral Fullerene Containing Electron Donor-Acceptor Complexes Utilized In Organic Photovoltaics, Fatemeh Amerikheirabadi

Open Access Theses & Dissertations

Organic Donor &ndash Acceptor complexes form the main component of the organic photovoltaic devices (OPVs). The open circuit voltage of OPVs is directly related to the charge transfer excited state energies of these complexes. Currently a large number of different molecular complexes are being tested for their efficiency in photovoltaic devices. In this work, density functional theory as implemented in the NRLMOL code is used to investigate the electronic structure and related properties of these donor &ndash acceptor complexes. The charge transfer excitation energies are calculated using the perturbative delta self &ndash consistent field method recently developed in our group …

A Study Of The Optical And Negative Ion Properties Of Selected Chiral Molecules, Jason Michael Lambert

Doctoral Dissertations

Chirality is subtle geometric property where objects lack reflection plane symmetry. In this thesis I study three chiral molecules using a combination of experimental and theoretical methods to elucidate the relationships between conformation freedom, solvent choice, and temperature. The importance of nuclear motion when predicting the optical rotation is explored. For carvone, corrections with each nuclear mode coordinate is important. Predictions of the ORD have the incorrect sign without the inclusion of vibrational corrections. For the case of two newly synthesized amino acid derivatives the vibrational corrections did not correct the sign of the calculated ORD to bring it into …

Ab-Initio And Model Studies Of Spin Fluctuation Effects In Transport And Thermodynamics Of Magnetic Metals, James K. Glasbrenner

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Magnetic materials are vital to many devices and the manipulation of spins is central to the operation of novel devices such as spin transistors. It is important to understand the effect of spin fluctuations on such systems. In this dissertation, first-principles calculations and models further the understanding of spin fluctuation effects in the transport and thermodynamics of magnetic metals.

A simple classical spin-fluctuation Hamiltonian with a single itinerancy parameter is studied using the mean-field approximation, Monte Carlo simulations, and a generalized Onsager cavity field method. The results of these different methods are in agreement. It is found that the thermodynamics …

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. …

A Non-Linear Eigensolver-Based Alternative To Traditional Self-Consistent Electronic Structure Calculation Methods, Brendan E. Gavin

Masters Theses 1911 - February 2014

This thesis presents a means of enhancing the iterative calculation techniques used in electronic structure calculations, particularly Kohn-Sham DFT. Based on the subspace iteration method of the FEAST eigenvalue solving algorithm, this nonlinear FEAST algorithm (NLFEAST) improves the convergence rate of traditional iterative methods and dramatically improves their robustness. A description of the algorithm is given, along with the results of numerical experiments that demonstrate its effectiveness and offer insight into the factors that determine how well it performs.