Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session Y03: Theoretical methods and studies |
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Sponsoring Units: DCP Chair: Jeffrey Owrutsky, Naval Research Lab Room: LACC 150C |
Friday, March 9, 2018 11:15AM - 11:27AM |
Y03.00001: Chaos in nanopores Vishal Nandigana, N. Aluru Nanofluidics has found itself in many applications ranging from water desalination, gas separation, fluidic circuits and DNA sequencing. In all these applications one of the important measuring signals is noise. Noisy signal disrupts the exact measuring signal in almost all of these applications. In this abstract, we rationalize whether current oscillations have to be classified only as noise or does the physical disturbance in ionic charges has some other meaning? We infer that the physical disturbance in ionic charges are not noise but can be viewed as chaos. Chaos is present in the system due to the depletion of the ions, created by the nonequilibrium an-harmonic electrostatic potential distribution, i.e., multi-potential wells are observed inside the nanopore. This multi-well potential distribution leads to bi-directional hopping of ions as the ions transport through the pore. The bi-directional hopping results in current oscillations. Thus, we say the notion of chaos exists from deterministic perspective. We prove this case by considering a simple oscillator model involving the electrostatic and dissipative forces to model ionic current. |
Friday, March 9, 2018 11:27AM - 11:39AM |
Y03.00002: Effective one-dimensional model for counter-ion flow through a viscoelastic, charged nanochannel Mpumelelo Matse, Michael Eikerling, Peter Berg In this work, we present a theoretical model for nonlinear deformational properties of the wall of a charged, viscoelastic nanochannel under the influence of water and ion flow. The nanochannel viscoelasticity is described by the Kelvin-Voigt model. Using continuum theories for mass and momentum conservation of the solid-liquid coupled system, we derive a set of 1-D nonlinear partial differential equations for the dynamics of the system. By means of linear perturbations and numerical calculations, the propagation properties of the fluid governed by these evolution equations are analysed in detail. Finally, we discuss one key application of this study: the dynamic response of polymeric membrane nanopores to the flow of water and protons in polymer electrolye membrane (PEM) fuel cells. |
Friday, March 9, 2018 11:39AM - 11:51AM |
Y03.00003: Geometric effects on fluctuating droplets in curved surfaces Eric Horsley, Maxim Lavrentovich, Randall Kamien Nucleation processes occur during first-order transitions and arise because of the metastability of a preexisting phase; a phenomenon ubiquitous in nature. Considering an order parameter with a prescribed Landau-Ginzburg energy, which may represent the relative density of liquid-vapor phases or the degree of crystallization of uniform-crystalline phases, we move to an interface representation of the nucleated droplets. By an expansion in small perturbations away from circular droplets we investigate the effects of the underlying geometry on the line tension arising from thermal fluctuations. |
Friday, March 9, 2018 11:51AM - 12:03PM |
Y03.00004: DFT Calculations of Motional Effects on NQR Parameters in Molecular Crystals Allen Majewski, Chris Billman, Hai-Ping Cheng, Neil Sullivan The ^{35}Cl and ^{14}N NQR frequencies in paradichlorobenzene and β- HMX are predicted at a variety of temperatures using density functional theory (DFT) and a general method is presented for first principles DFT calculations of the temperature dependent NQR spectra in molecular crystals. Crystal cells of various volumes corresponding to experimental cell parameters are derived and a sequence of atomic configurations are generated from molecular dynamics (MD) at each volume. The principal axes of the electric field gradient (EFG) tensors are computed for each configuration. The temperature dependence of the NQR frequencies are then computed geometrically from expressions relating the EFG tensor of a rotated system to that of a fixed system through rotations about the principle axes. The method simultaneously accounts for the volume dependence of the EFG due to thermal expansion, as well as the T-dependence of the EFG through internal motions, allowing a first-principles calculation of the isobaric NQR T-dependence using only experimental structural data. The method does not depend on the particulars of the crystal structure or require any insight as to the nature of the internal motions. |
Friday, March 9, 2018 12:03PM - 12:15PM |
Y03.00005: Computation of ground-state properties in molecular systems:
back-propagation with auxiliary-field quantum Monte Carlo Mario Motta, Shiwei Zhang The quantitative study of correlated materials requires accurate calculation of electronic density, |
Friday, March 9, 2018 12:15PM - 12:27PM |
Y03.00006: Quantum Thermodynamics for Driven Dissipative Bosonic Systems Maicol Ochoa, Natalya Zimbovskaya, Abraham Nitzan The formulation of thermodynamic concepts applicable to molecular and nanoscale devices has motivated intense research, as such systems provide a unique setting to study heat transfer, power work and dissipation far from the thermodynamic limit. In the quantum regime, dynamics, broadening of energy levels and interference can play important roles and have been studied within the emerging field of quantum thermodynamics. In this talk we describe recent results in the study of two prototypical dissipative bosonic systems under slow driving and arbitrary system-bath coupling strength. Specifically, we look at the damped harmonic oscillator and the damped two-level system. For the former, we study independently the slow time-dependent perturbation in the oscillator frequency and in the coupling strength. For the latter, we concentrate on the slow modulation of the energy gap between the two levels. Importantly, we are able to find the entropy production rates for each case without explicitly defining nonequilibrium extensions for the entropy functional. This analysis also permits the definition of phenomenological friction coefficients in terms of structural properties of the system-bath composite. |
Friday, March 9, 2018 12:27PM - 12:39PM |
Y03.00007: Diffusion quantum Monte Carlo study of halogen and chromium-halogen complexes Allison Dzubak, Jaron Krogel, Valentino Cooper, Fernando Reboredo Diffusion quantum Monte Carlo (DMC) has emerged as an accurate method to predict the structural, electronic, magnetic, and defect properties of strongly-correlated transition metal oxides. We are extending the application of DMC to layered materials with the formula CrX_{3} (X = F, Cl, Br and I) which have potential spintronic and biomedical applications. In order to establish the accuracy of our theoretical predictions for CrX_{3}, we must first carefully examine and estimate all errors in DMC. The use of pseudopotentials, although necessary for large systems, introduces errors. In this work, we test the performance of two sets of DMC pseudopotentials for halogen and chromium-halogen complexes. Using validated pseudopotentials, we contribute to the understanding of structural and vibrational properties of CrF_{2} and CrF_{3} molecules. |
Friday, March 9, 2018 12:39PM - 12:51PM |
Y03.00008: FLO-SIC atomic orbital energies Kai Trepte, Kushantha Withanage, Juan Peralta, Koblar Jackson Given the Fermi-Löwdin orbital self-interaction correction (FLO-SIC), many short-comings of standard density functional theory (DFT) are corrected. It has been shown for example in [1,2] that FLO-SIC corrects the HOMO energy level and level ordering of standard DFT in comparison to experiment. |
Friday, March 9, 2018 12:51PM - 1:03PM |
Y03.00009: Visualization of dissipative wavepacket dynamics at conical intersections Lipeng Chen, Maxim Gelin, Wolfgang Domcke The effect of a dissipative thermal environment on the ultrafast nonadiabatic dynamics at conical intersections is nowadays well understood. Yet, the molecular wavepacket dynamics at conical intersections has not been directly characterized and monitored via femtosecond nonlinear spectroscopy. Transient absorption pump-probe spectroscopy with white-light continuum detection has recently reached a 5-10 fs time resolution, which enables a direct characterization of molecular wavepackets possessing multiple vibrational modes. We have combined the hierarchy equation of motion with the equation-of-motion phase-matching approach to simulate pump-probe and fluorescence up-conversion signals for a model of S_{2}(ππ*)-S_{1 }(nπ*) conical intersection in pyrazine which is bilinearly coupled to a harmonic bath with Drude spectral density function. Our results show that the signals indeed visualize evolutions of the wave packet at conical intersections, and these evolutions are quite sensitive to the bath parameters as well as to the envelope of the laser pulses. |
Friday, March 9, 2018 1:03PM - 1:15PM |
Y03.00010: Anisotropic carrier mobility in two-dimensional materials with tilted Dirac cones: theory and application Ting Cheng We have theoretically investigated the intrinsic carrier mobility in semimetals with tilted Dirac cones under both longitudinal and transverse acoustic phonon scattering. An analytical formula for the carrier mobility was obtained. It shows that tilting significantly reduces the mobility. The theory was then applied to 8B-Pmmn borophene and borophane (fully hydrogenated borophene), both of which have tilted Dirac cones. The predicted carrier mobilities in 8B-Pmmn borophene at room temperature are 14.8×10^{5}and 28.4×10^{5} cm^{2} V^{-1} s^{-1} along the x and y directions, respectively, both of which are higher than that in graphene. For borophane, despite its superhigh Fermi velocity, the carrier mobility is lower than that in 8B-Pmmn owing to its smaller elastic constant under shear strain. |
Friday, March 9, 2018 1:15PM - 1:27PM |
Y03.00011: Molecular, spectral and electronic analysis of three isomeric
benzotriazolylpropanamides using theoretical approaches Meryem Evecen The small amounts of isomeric benzotriazolylpropanamides (2-methyl-3-(1H-benzotriazol-1-yl)propanamide, 2-methyl-3-(2H-benzotriazol-2-yl)propanamide and N,N-dimethyl-3-(1H-benzotriazol-1-yl)propanamide) compounds [1] molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13C -NMR chemical shift values and electronic properties in the ground state were investigated using the density functional theory methods (HF, B3LYP) with 6-311++G(d,p) basis set [2]. The electric dipole moment (μ), polarizability (α) and the first hyperpolarizability (β) values of the compound were calculated theoretically. The first hyperpolarizability of the molecule shows that the compound can be a good candidate of nonlinear optical material. In addition, molecular electrostatic potential (MEP) and frontier molecular orbital energies were also performed at HF,B3LYP/6-311++G(d,p) level of theory. The theoretical results show good agreement with experimental values. |
Friday, March 9, 2018 1:27PM - 1:39PM |
Y03.00012: Atomic forces in Fermi-Löwdin local orbital self-interaction correction calculations Koblar Jackson, Kai Trepte, Kushantha Withanage, Der-you Kao, Juan Peralta We present a derivation of atomic forces for density functional theory calculations with the Perdew-Zunger self-interaction-correction. The forces consist of the Hellmann-Feynman contributions and the Pulay corrections that are required when an atom-centered basis set is used. The method has been incorporated in the FLO-SIC code, which implements the Fermi-Löwdin local orbital (FLO) approach to the self-interaction correction (SIC). We present results of using this method for several small molecules and show that they agree well with corresponding results obtained using finite differences of self-consistent total energies. We also show the results of using the calculated forces to optimize molecular geometries in FLO-SIC. |
Friday, March 9, 2018 1:39PM - 1:51PM |
Y03.00013: Light-matter interaction in the long-wavelength limit: necessity of the dipole self-energy. Vasil Rokaj, Davis Welakuh, Michael Ruggenthaler, Angel Rubio Most theoretical studies for correlated light-matter systems are performed within the long-wavelength limit, i.e., the electromagnetic field is assumed to be spatially uniform. In this limit the so-called length-gauge transformation for a fully quantized light-matter system gives rise to the dipole self-energy of the electrons. In practice this term is often discarded as it is assumed to be subsumed in the kinetic energy term. In this presentation we show the necessity of the dipole self-energy term. First and foremost, without it the light-matter system in the long-wavelength limit does not have a ground-state. Further implications of the dipole self-energy will be presented, such as the change of the translation operator and how this influences the Bloch theorem. |
Friday, March 9, 2018 1:51PM - 2:03PM |
Y03.00014: Hubbard Interactions From Density-Functional Perturbation Theory Iurii Timrov, Matteo Cococcioni, Nicola Marzari DFT+U is a simple and powerful tool to model systems containing partially-filled manifolds of localized states. However, the Hubbard parameters are often treated semi-empirically, which is a somewhat unsatisfactory approach. Conceptual methods to determine U from first principles have nevertheless been introduced long ago, based either on the constrained random-phase approximation or linear-response theory. These approaches make DFT+U a fully self-contained method but are often overlooked due to their cost or complexity. We introduce a computationally inexpensive and straightforward approach to determine the linear-response U, hitherto obtained from the difference between bare and self-consistent inverse electronic susceptibilities evaluated from supercell calculations. By recasting these calculations in the language of density-functional perturbation theory we remove the need of supercells, and allow for a fully automated determination of susceptibilities and Hubbard parameters. Such developments open the way for deployment in high-throughput studies, can be extended to intersite couplings V, while providing the community with a simple tool to calculate consistent values of U for any system at hand. Last, the approach is showcased with applications to transition-metal compounds. |
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