Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J21: Advances in Computational PhysicsLive

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Sponsoring Units: DCOMP Chair: Khadijeh Najafi, IBM TJ Watson Research Center 
Tuesday, March 16, 2021 3:00PM  3:12PM Live 
J21.00001: Replacing the linear Schröding equation for a quantum state with a nonlinear equation for the local information Thomas Klein Kvorning In this talk, I will show how one can timeevolve local information, i.e., the local density matrices of a system, in a closed way, without invoking the full state of the system. 
Tuesday, March 16, 2021 3:12PM  3:24PM Live 
J21.00002: Quantum Monte Carlo Results for Rényi Entanglement Entropy in the BoseHubbard Model Emanuel CasianoDiaz, Chris M Herdman, Adrian G Del Maestro In this talk we report Rényi Entanglement Entropies in the Ddimenisional BoseHubbard Model computed via quantum Monte Carlo simulations. We discuss algorithmic extensions of the T = 0 path integral quantum Monte Carlo framework that make this possible, and allow for the study of Rényi entanglement entropies in bosonic lattice models in general spatial dimensions with favorable polynomial scaling with system size. Some applications of this new technology include probing quantum phase transitions, quantifying the entanglement accessible as a resource for quantum computing, and exploring the scaling of spatial entanglement with subregion size. 
Tuesday, March 16, 2021 3:24PM  3:36PM Live 
J21.00003: Quantum caustics in the dynamics of the three mode BoseHubbard model Wyatt Kirkby, Duncan O'Dell Caustics are a naturally occurring wave focusing phenomenon that is well known in optics and hydrodynamics. Their significance lies in the fact that they dominate wavefields in the short wavelength limit and have universal properties including a hierarchy of characteristic shapes 
Tuesday, March 16, 2021 3:36PM  3:48PM Live 
J21.00004: Scrambling and chaos in quantum spin chains: insights from matrix product states Chengshu Li, Anna Keselman, Etienne LantagneHurtubise We develop an approach to investigate scrambling, as measured by outoftimeorder correlators (OTOCs), in onedimensional quantum systems. The approach is based on thermofield double states and is closely related to the standard purification method for the simulation of finitetemperature equilibrium properties using matrix product states. However, it presents a number of computational advantages which we detail here. We apply the method to the paradigmatic 1D quantum Heisenberg model and evaluate its OTOCs for different spin representations S up to 5. The explicit treatment of the nonAbelian SU(2) symmetry allows to compute OTOCs for intermediate time scales and large system sizes. As S increases we find a "quantum to classical" crossover where the OTOCs starts to exhibit a period of exponential growth with a Lyapunov exponent λ_{L}, thus corroborating a recent conjecture in the literature. 
Tuesday, March 16, 2021 3:48PM  4:00PM Live 
J21.00005: On the Unification of Nature’s Complexities via a Matrix Permanent:
Critical Phenomena, Fractals, Quantum Computing, #P/NPComplexity Vitaly Kocharovsky, Vladimir Kocharovsky, Sergey Tarasov We find a remarkable explicit connection between the major types of complexity in nature [Entropy 22, 322 (2020)]. They represent the critical phenomena, fractal structures in the theory of chaos, quantum information processing in manybody physics, cryptography, numbertheoretic complexity in mathematics, and #Pcomplete problems. We show that all of them are analytically related to a wellknown in mathematics matrix permanent via the fractal Weierstrasslike functions and polynomials or determinants involving complex variables. We discuss the #P/NPcomplexity of quantum computing, nontrivial reduction of the critical phenomena problem to a permanent, new integral representations of the permanent revealing its relation to fractals and chaos, complex stochastic multivariate polynomials, numbertheoretical functions, asymptotics of a Toeplitz determinant employed in the Onsager’s solution of the Ising model and given by the Szego limit theorems. 
Tuesday, March 16, 2021 4:00PM  4:12PM Live 
J21.00006: Vacancy elastodiffusion around cavities in aluminium: Fast first passage algorithms based on Krylov subspace projection techniques Savneet Kaur, Manuel Athènes, Jérôme Creuze The Kinetic Monte Carlo method is widely used in material science to simulate the microstructural evolution of alloys under irradiation. This approach is based on a master equation and a transition rate matrix. The KMC method is inefficient when the transition rate matrix exhibits a wide spectrum of frequencies. Defects perform a huge number of transitions between atomic configurations which are connected by small energy barriers. They form trapping basins; the system remains trapped in metastable thermodynamic states. Acceleration methods based on the theory of absorbing Markov Chains are available to overcome this issue in the KMC method. The escaping events are characterized by their first passage and nopassage distributions. Assuming the diffusion processes are reversible, a property satisfied by the dynamics of defects in metals and alloys, we show that the involved eigenvalue problems to be solved can be symmetrized. We illustrate the performance of a tool based on Krylov subspace by computing sink strengths for the emission and absorption of vacancies from and to cavities in aluminium^{1,2}. 
Tuesday, March 16, 2021 4:12PM  4:24PM Live 
J21.00007: Determining the potential of ZnO surfaces for FischerTropsch synthesis using Car–Parrinello molecular dynamics Charith DeSilva We investigate the performance of nonpolar ZnO surfaces as a catalyst in FischerTropsch synthesis (FTS) through CarParrinello molecular dynamics. Economic and environmental concerns regarding the future of fuel production have increased interest in viable FTS catalysts. ZnO nanoparticles are promising catalytic candidates as they are environmentally safe and costeffective. While the polarsurfaces of ZnO have been heavily studied, the nonpolar surfaces have not. We computationally investigate the adsorption properties of various molecules vital to the FTS process over the pristine and defect nonpolar ZnO surfaces. All molecular dynamics calculations were carried out with van der Waals exchangecorrelation pseudopotentials in order to fully understand the adsorption process. From the results of the molecular dynamics simulations we propose that the ZnO dimerdefect surfaces can absorb and break the bonds of certain molecules, which is vital to the FTS process. We also observed weak interactions between both the dimer and edgedefect surfaces. These results show promise for ZnO defectsurfaces as FTS catalysts and showcase the effectiveness of molecular dynamics in visualizing the adsorption process. 
Tuesday, March 16, 2021 4:24PM  4:36PM Live 
J21.00008: Molecular Simulation of Gas Transport Through Cylindrical Pores Yue Yu, Kai Zhang Recent developments in selfassembled block copolymers make it possible to synthesize regular porous nanofiltration membranes, which could potentially push the separation limit of gas mixtures. While experimental and theoretical efforts have been made to investigate this problem, a quantitative understanding is still missing. We perform molecular dynamics simulation of binary hard spheres diffusing through rigid membranes filled with cylindrical pores. Particle diffusivity is found to be proportional to pore size, following the Knudsen diffusion mechanism. A powerlaw tradeoff relationship between permeability and selectivity is obtained, which is consistent with the Freeman theory of gas separation via disordered polymeric membranes. The dependence of the upper bound limit on the size ratio of gas particles is extracted. The effect of polydispersity on membrane pore size is examined. 
Tuesday, March 16, 2021 4:36PM  4:48PM Live 
J21.00009: Photoionization of Ca~XVIIXIX Sultana Nahar Characteristic features of photoionization of He and Lilike Ca, Ca~XVII and Ca~XIX,`have been studied using the relativistic BreitPauli Rmatrix method and close coupling approximation. Photoionization cross sections $\sigma_{PI}$ of both ions show monotonic decrease from threshold to high energies as the core excitations lie in the high energy. Resonances begin with K$_{\alpha}$ excitations. Rydberg series of resonances due to n=2 excitations dominate photoionization. Beyond n=2 excitations resonances 
Tuesday, March 16, 2021 4:48PM  5:00PM Live 
J21.00010: Analytical theory of a selfconsistent magnetopause in a collisionless plasma Vladimir Kocharovsky, Vitaly Kocharovsky, Vladimir Martyanov, Anton Nechaev An analytical model of a quasistationary current sheet that separates the regions of weakly and strongly magnetized collisionless plasma and describes the magnetopause formed by the solar (stellar) wind is presented. The model significantly expands the scope of a magnetohydrodynamic approach and is based on the consistent kinetic description of the inhomogeneous anisotropic distribution functions of electrons and ions with different effective temperatures. Its detailed analysis for the shifted Maxwell, kappa and other particle distributions with different anisotropy degrees is carried out. A qualitative comparison of the predicted and observed spatial current profiles in the Earth's magnetopause is given. 
Tuesday, March 16, 2021 5:00PM  5:12PM Live 
J21.00011: Modelling of interplanetary magnetic clouds evolution. Cristian Bahrim, Talon Weaver, Evgeny Romashets In this work, we study changes of magnetic cloud shapes on their travel from the solar corona to the Earth’s orbit. Magnetic field at the origin of the cloud is determined from WSO source surface maps. Velocity of ambient solar wind is approximated by Parker’s formula adjusted for interplanetary plasma measurements at 1 AU. Solar wind density profile is set to satisfy flow continuity requirement. The cloud expands once the total ambient pressure decreases on its motion. There are two constrains for the expansion: conservation of total magnetic energy density inside the magnetic cloud and conservation of the magnetic flux at the boundary of the cloud. Our model leads to the dependence of minor and major radii of the cloud to the heliodistance. We will show typical profiles for fast and slow magnetic clouds observed in 19982001. 
Tuesday, March 16, 2021 5:12PM  5:24PM Live 
J21.00012: A Covariant Field Reformulation of Classical Electrodynamics William Maier Classical electrodynamics is here reformulated as a field theory rather than a particle and field theory. Electromagnetic fields are taken to be continuous and differentiable everywhere. Maxwell’s equations are assumed to be valid at all scale lengths, and second order variations on the vector potentials A_{k} are used to obtain fundamental equations from a covariant action in which the usual term involving particle mass m has been replaced by the covariant mass density µ associated with the fields. These equations lead directly to the Lorentz force plus radiation reaction and to equations from which static charge distributions having finite extent and charge of only one sign are found. These bodies are stabilized by the charge motion in the distribution’s selffield. Their mass is finite and equivalent to the energy of the electromagnetic field integrated over all space. Spin, magnetic moment, and electric dipole and quadrupole moments of these bodies can be calculated. Ordinary classical electromagnetism is thus reproduced without point charges, and the classical structures of fundamental charged bodies may be obtained. Structure of the electron in this theory is briefly discussed. 
Tuesday, March 16, 2021 5:24PM  5:36PM Live 
J21.00013: Efficient Parallelization Scheme for Periodic Coupled Cluster Theory Yang Gao, Phillip Helms, Edgar Solomonik, Garnet Chan We present a novel strategy for tensor contractions in periodic coupled cluster theory. The scheme is based on transformation of irreducible representations and efficiently handles the translational symmetry in periodic wavefunction methods. Preliminary benchmarking results on periodic CCSD and CCSD(T) will be presented. 
Tuesday, March 16, 2021 5:36PM  5:48PM On Demand 
J21.00014: Facile Phase Retrieval with Vector Angular Momentum Beams Gaurav Ahuja, Baurzhan Muminov, Luat Vuong Solutions to the "phase problem" are broadly classified into phase retrieval using masks, interferometry and ptychography, which generally involve moving parts or iterative algorithms. Iterative algorithms, such as Gerchberg–Saxton and Yang–Gu, are reliable but slow to converge and often computational demanding. Interferometric methods are computationally simpler but require a more complex experimental setup. Ptychographic methods involve a more developed experimental setup with a probe beam and typically an iterative algorithm. In this paper we demonstrate a noninterferometric, noniterative, experimentally and computationally simple method for phase retrieval using an ellipticallypolarized vortex vector beam. Light from different locations of the illuminating vortex beam are phase locked and interfere in the diffraction measurement to produce differentiation in the Fourier plane. As a result, the phase calculation may be reduced to simple addition and subtraction of gradient terms from filtered intensity patterns of the vortex profile. We derive partial differential equations consisting of spatial gradients corresponding to the vortex illumination for phase retrieval calculations. This makes our noninterferometric method among the simplest to date. 
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