Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L27: Electronic Structure Methods III |
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Sponsoring Units: DCOMP Chair: James Shepherd, Rice University Room: 501 |
Wednesday, March 5, 2014 8:00AM - 8:12AM |
L27.00001: Probing the electronic structure of liquid water with many-body perturbation theory Tuan Anh Pham, Cui Zhang, Eric Schwegler, Giulia Galli We present a first-principles investigation of the electronic structure of liquid water based on many-body perturbation theory (MBPT), within the G$_0$W$_0$ approximation. The liquid quasiparticle band gap and the position of its valence band maximum and conduction band minimum with respect to vacuum were computed and it is shown that the use of MBPT is crucial to obtain results that are in good agreement with experiment. We found that the level of theory chosen to generate molecular dynamics trajectories may substantially affect the electronic structure of the liquid, in particular, the relative position of its band edges and redox potentials. Our results represent an essential step in establishing a predictive framework for computing the relative position of water redox potentials and the band edges of semiconductors and insulators.\\[4pt] [1] T. Anh Pham, C. Zhang, E. Schwegler and G. Galli (submitted). [Preview Abstract] |
Wednesday, March 5, 2014 8:12AM - 8:24AM |
L27.00002: Hybrid DFT First-Principles Study of the Properties of Water Martin Schlipf, Francois Gygi Water plays a crucial role in many chemical and biological reactions. Hence, an accurate description of the properties of water is imperative for a detailed understanding of these reactions. In recent years, hybrid density functionals such as PBE0 and HSE06 have improved the accuracy of DFT calculations for many insulators and semiconductors, as well as for aqueous solutions[1]. However, the evaluation of the Hartree Fock (HF) exchange energy makes these functionals computationally very demanding. We present a comparison of the structural and electronic properties of water obtained using the PBE0 and HSE06 density functionals. Simulations were performed using the Qbox code[2], and a recursive bisection scheme[3] reducing the computational cost of HF integrals. We discuss the effect of this approximation on the accuracy and the computation time, and compare our results to related work[4-5]. \\{} [1] C. Zhang, {\it et al.}, J. Chem. Phys. {\bf 138}, 181102 (2013).\\{} [2] http://eslab.ucdavis.edu/software/qbox \\{} [3] F. Gygi and I. Duchemin, J. Chem. Theory Comput. {\bf 9}, 582 (2012).\\{} [4] T. Todorova, {\it et al.}, J. Phys. Chem. B {\bf 110}, 3685 (2006).\\{} [5] M. Guidon, {\it et al.}, J. Chem. Phys. {\bf 128}, 214104 (2008). [Preview Abstract] |
Wednesday, March 5, 2014 8:24AM - 8:36AM |
L27.00003: Accurate calculation of the x-ray absorption spectrum of water via the GW/Bethe-Salpeter equation Keith Gilmore, John Vinson, Josh Kas, Fernando Vila, John Rehr We calculate x-ray absorption spectra (XAS) of water within the OCEAN code, which combines plane-wave, pseudopotential electronic structure, PAW transition elements, GW self-energy corrections, and the NIST BSE solver [1]. Due to the computational demands of this approach, our initial XAS calculations were limited to 17 molecule super cells [2]. This lead to unphysical, size dependent effects in the calculated spectra. To treat larger systems, we extended the OCEAN interface to support well-parallelized codes such as QuantumESPRESSO. We also implemented an efficient interpolation scheme of Shirley. We applied this large-scale GW/BSE approach to 64 molecule unit cell structures of water obtained from classical DFT/MD and PIMD simulations [3]. In concurrence with previous work [4], we find the calculated spectrum both qualitatively and quantitatively reproduces the experimental features. The agreement implies that structures based on PIMD, which are similar to the traditional distorted tetrahedral view, are consistent with experimental observations. \\[4pt] [1] J. Vinson et al., PRB 83, 115106 (2011); J. Vinson and J.J. Rehr, PRB 86, 195135 (2012). [2] J. Vinson et al., PRB 85, 045101 (2012). [3] J.A. Morrone and R. Car, PRL 101, 017801 (2008). [4] L. Kong et al., PRB 86, 134203 (2012). [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 8:48AM |
L27.00004: Sum frequency generation spectra of ice surfaces from first principles simulations Quan Wan, Francois Gygi, Giulia Galli The morphology and structure of ice surfaces play an important role in a variety of chemical and physical processes. Yet a detailed knowledge of the structural properties of ice surfaces at the molecular level is still lacking. Sum frequency generation (SFG) spectroscopy is a promising technique to address this problem, due to its high interface sensitivity. Here we present first principles simulations of SFG spectra of ice surfaces obtained by \textit{ab initio} molecular dynamics, combined with density functional perturbation theory (DFPT), as implemented in the Qbox Code. We computed SFG signals from classical time correlation functions of the system's dipole moment and polarizability tensor, evaluated by using maximally localized Wannier functions and DFPT. By projecting the total SFG intensities onto each molecules, we analyzed the stretching band region of the SFG spectra and identified intra- and inter-bilayer modes. This analysis was then used to shed light on whether the ice surface is proton ordered or disordered. In addition to ice, we will also discuss simulations of SFG signals obtained for solid-water interfaces using the same \textit{ab initio} method. [Preview Abstract] |
Wednesday, March 5, 2014 8:48AM - 9:00AM |
L27.00005: Energy Level Alignment at Aqueous GaN and ZnO Interfaces Mark S. Hybertsen, Neerav Kharche, James T. Muckerman Electronic energy level alignment at semiconductor-electrolyte interfaces is fundamental to electrochemical activity. Motivated in particular by the search for new materials that can be more efficient for photocatalysis, we develop a first principles method to calculate this alignment at aqueous interfaces and demonstrate it for the specific case of non-polar GaN and ZnO interfaces with water. In the first step, density functional theory (DFT) based molecular dynamics is used to sample the physical interface structure and to evaluate the electrostatic potential step at the interface. In the second step, the GW approach is used to evaluate the reference electronic energy level separately in the bulk semiconductor (valence band edge energy) and in bulk water (the 1b$_{1}$ energy level), relative to the internal electrostatic energy reference. Use of the GW approach naturally corrects for errors inherent in the use of Kohn-Sham energy eigenvalues to approximate the electronic excitation energies in each material. With this predicted interface alignment, specific redox levels in water, with potentials known relative to the 1b$_{1}$ level, can then be compared to the semiconductor band edge positions. Our results will be discussed in the context of experiments in which photoexcited GaN and ZnO drive the hydrogen evolution reaction. [Preview Abstract] |
Wednesday, March 5, 2014 9:00AM - 9:12AM |
L27.00006: Structural and electronic properties of NaCl dissolved in water Alex P. Gaiduk, Francois Gygi, Giulia Galli We carried out \emph{ab initio} molecular dynamics simulations of a 1 M NaCl aqueous solution with the \emph{Qbox} code, using the hybrid functional PBE0 and the bisection technique introduced in Ref.~[1] to compute the Hartree--Fock exchange. We performed both NVT and NVE simulations. We found that the position of the Cl$^-$ and Na$^+$ energy levels is considerably improved compared to the one obtained using the PBE functional, and that the anion highest occupied orbital [2] is unaffected by the presence of the sodium counterion. We also found that the average properties obtained in the NVE ensemble and those computed in the NVT ensemble with the Bussi--Donadio--Parrinello thermostat [3] are the same, within the statistical error bars of our simulations.\\[4pt] [1] F. Gygi and I. Duchemin, \emph{J.~Chem.\ Theory\ Comput.} \textbf{9}, 582 (2013).\\[0pt] [2] C. Zhang, T. Anh Pham, F. Gygi, and G. Galli, \emph{J.~Chem.\ Phys.} \textbf{138}, 181102 (2013).\\[0pt] [3] G. Bussi, D. Donadio, and M. Parrinello, \emph{J.~Chem.\ Phys.} \textbf{126}, 014101 (2007). [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:24AM |
L27.00007: \textit{Ab-Initio} Calculations of the Electronic Properties of Boron Nitride Anthony Stewart, Bethuel Khamala, Daniel Hart, Diola Bagayoko The potential of Boron Nitride (BN) in nanotechnology is tremendous. BN in its bulk form has a wide band gap with excellent thermal and chemical stability. BN structures can be tailored using various techniques in order to obtain desired materials properties. The State-of-the-art Proton Exchange Membrane Fuel Cell (PEMFCs) technology exploits graphitized carbon as a support for platinum-type catalysts.~ However, some forms of carbon are susceptible to long-term durability issues such as corrosion which is a detriment to fuel cell performance and viability. Novel non-carbon supports such as BN may provide a pathway for addressing the durability and performance issues associated with carbon support materials. We present preliminary theoretical studies, using an linear combination of atomic orbital (LCAO) quantum chemistry package from Ames Laboratory, of the electronic properties of this potentially important material. Our calculated band gap of 6.48 eV for the cubic structure, obtained with an LDA potential and the BZW-EF method, is in agreement with experiment. [Preview Abstract] |
Wednesday, March 5, 2014 9:24AM - 9:36AM |
L27.00008: Ab-initio atomic level stresses in Cu-Zr systems Madhusudan Ojha, Don M. Nicholson, Takeshi Egami In our recent studies [D. M. Nicholson, Madhusudan Ojha and Takeshi Egami, J. Phys.: Condens. Matter 25 435505 (2013)] we have calculated ab-initio atomic level stresses in the simple B2 Cu-Zr system, Cu50Zr50 liquid and glass and have found tremendous atomic level stress in the B2 structure due to strong bonding between Cu and Zr and significantly smaller atomic level stresses in liquid and glass due to reduced chemical order. We have extended our studies to additional structures and stoichiometries. On the basis of these results we discuss the relationship between short-range order, bonding, electronic density of states and atomic level stress. We are searching for an explanation of the unique position of Zr as a promotor of glass forming ability. We report the differences in atomic level stress, bonding, and density of states when Ti, Y, and Nb replace Zr on fixed structures. [Preview Abstract] |
Wednesday, March 5, 2014 9:36AM - 9:48AM |
L27.00009: Ab initio DFT calculations of vibrational properties S.M. Story, F.D. Vila, J.J. Kas, J.J. Rehr Vibrational properties such as EXAFS and crystallographic Debye-Waller factors, vibrational free energies, phonon self-energies, and phonon contributions to the electron spectral function, are key to understanding many aspects of materials beyond ground state electronic structure. Thus, their simulation using first principles methods is of particular importance. Many of these vibrational properties can be calculated from the dynamical matrix and electron-phonon coupling coefficients obtained from DFT calculations. Here we present a code DMVP [1] that calculates these properties from the output of electronic structure codes such as ABINIT, Gaussian, Quantum Espresso and VASP. Our modular interfacing tool AI2PS allows us to translate the different outputs into a DMVP compatible format and generate vibrational properties in an automated way [2]. Finally, we present some current applications that take advantage of the modular form of AI2PS to extend its capabilities to the calculation of coefficients of thermal expansion and other properties of interest such as infrared spectra. \\[4pt] [1] F. D. Vila et al., Phys. Rev. B {\bf 76}, 014301 (2007). \\[0pt] [2] J.J. Rehr et al., C. R. Physique {\bf 10} (2009). [Preview Abstract] |
Wednesday, March 5, 2014 9:48AM - 10:00AM |
L27.00010: End-group Influence on the Frontier Molecular Orbital Reorganization in Molecular Junctions --- Effect on Thermopower Janakiraman Balachandran, Pramod Reddy, Barry Dunietz, Vikram Gavini The frontier molecular orbital (FMO) reorganization and in turn on the thermopower of the aromatic molecules trapped between metal electrodes (aka molecular junctions) depends on two effects namely (1) the stabilization effect -- due to the physical presence of the metal electrode atoms and (2) change in e-e interactions -- due to end-group mediated charge transfer. The stabilization effect always reduces the FMO energies. The charge transfer effect increases the FMO energies in charge-gaining molecules, which in turn opposes the stabilization effect resulting in a small overall shift. However, the charge transfer effect decreases the FMO energies in charge-losing molecules, which in turn complements the stabilization effect resulting in a large overall downward shift. This hypothesis is validated by delineating the shifts due to stabilization and charge-transfer effects independently. Further we also demonstrate the generality of the hypothesis by applying it on a wide range of aromatic molecules with different length and end-groups. Finally, we also present computationally efficient strategies, based on the proposed mechanism, to quantitatively compute the FMO reorganization which in turn has potential for high throughput analysis of molecular junctions. [Preview Abstract] |
Wednesday, March 5, 2014 10:00AM - 10:12AM |
L27.00011: Momentum-dependent local ansatz approach to correlated electrons Yoshiro Kakehashi, Sumal Chandra, M. Atiqur R. Patoary Variational approach has been a simple and useful tool to describe the ground state of correlated electrons in solids, and many methods as well as wavefunctions for electron correlations have been proposed. Although the numerical methods such as the variational Monte-Carlo can quantitatively describe the correlations in the low dimensional system, the description of the real 3D system based on the wavefunction method has not yet been established well. We present here the momentum-dependent local ansatz approach (MLA) to the correlated electron system. The wavefunction consists of the two-particle excitation operators with momentum-dependent variational parameters, which are projected onto local orbitals, and a hybrid wavefunction which interpolates between the Hartree-Fock and the Hubbard alloy-analogy wavefunctions. On the basis of the numerical calculations in infinite dimensions, we demonstrate that the analytic MLA improves the Gutzwiller method in both the weak and strong interaction regimes, and that the MLA is applicable to the realistic systems with use of the 1st-principles LDA+U Hamiltonian. [Preview Abstract] |
Wednesday, March 5, 2014 10:12AM - 10:24AM |
L27.00012: Effects of local atomic environment and atomic long range order on magnetism in Fe-Al alloys Sergii Khmelevskyi Using first-principle Local Self-Consistent Green Function (LSGF) method and Local Spin Density Approximation we have studied local environment effects on magnetism of Fe in FeAl alloys near and at 1:1 atomic composition. The long range atomic order (LRO) in the alloys has been varied from complete disorder (A1) to full order (B2). We have derived the dependence of the Fe magnetic moments on local atomic environment up to second nearest neighbor (NN) shell, which is found to exhibit a highly not-trivial behavior. In order to explain a sharp difference in the magnetic behavior of ordered and disordered Fe-Al alloys we calculate the inter-atomic magnetic exchange interactions and their dependence on the state of the atomic LRO using conventional Lichtenstein formalism. We have found strong antiferromagnetic interactions between Fe atoms on long distance NN shells of underlying bcc lattice, which compete in size with ferromagnetic one on the first NN shells. The magnitude of these interactions is strongly depending on the state of the atomic LRO and this effect is the reason for onset of few different spin-glass regimes in the partially ordered Fe-AL alloys. [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L27.00013: Applications of DFT to Lanthanides and Precious Metal Complexes Alex Balboa, Margaret Hurley, Amanda Jenkins Density functional theory is widely used for computational characterization of novel materials. While study of materials containing the lighter elements is commonplace, the application of these methods to the bottom of the periodic table, including the lanthanides and the heavier precious metals such as Osmium, requires careful validation. Here we present results of recent quantum mechanical studies to characterize Lanthanide/Graphene Materials and assess the suitability of DFT for these systems. Additionally, we will present recent work on similar application of DFT to characterize Os bipridine complexes. [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L27.00014: First-Principles Calculations of Magnetic Properties of MnBi doped with Co Chandani N. Nandadasa, Vivek Dikshith, Sungho Kim, Seong-Gon Kim, Jihoon Park, Yang-Ki Hong First principles total-energy calculations were performed to investigate the magnetic and electronic properties of MnBi doped with Co. We used Density Functional Theory (DFT) within the generalized gradient approximation (GGA) with Projector Augmented Wave (PAW) potentials. We found that when MnBi was doped with Co,the magnetization increased as the concentration of Co increased. We also calculated magnetic anisotropy energy (MAE) and magnetic anisotropy constant ($K_u$) of MnBi before and after doping Co. [Preview Abstract] |
Wednesday, March 5, 2014 10:48AM - 11:00AM |
L27.00015: Effect of Orbital Differentiation on Magnetism in the 111 iron-based superconductors Ming-Cui Ding, Yu-Zhong Zhang Though similar lattice and electronic structures were found in MgFeGe, LiFeAs and NaFeAs, distinct behaviors at low temperature were reported from experiments. While MgFeGe is nonmagnetic and non-superconducting down to $2$~K, LiFeAs is a good superconductor with T$_c=18$~K, which are in sharp contrast to NaFeAs where a magnetically driven structural phase transition above the superconducting transition is detected. By calculating orbitally resolved Pauli susceptibility, we conclude that the occurrence of magnetism and superconductivity in these materials can be well interpreted from the weak coupling limit provided orbital degrees of freedom are considered.The stronger magnetic instability appearing in the d$_{x^2-y^2}$ orbital is responsible for the occurrence of weak magnetism in NaFeAs, compared to the superconducting LiFeAs, while featureless q dependent magnetic instability is responsible for the nonmagnetism in MgFeGe. [Preview Abstract] |
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