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 X22: Computational Methods for Statistical Mechanics: Advances and Applications  IIIFocus Live

Hide Abstracts 
Sponsoring Units: DCOMP GSNP Chair: Markus Eisenbach, Oak Ridge National Lab 
Friday, March 19, 2021 8:00AM  8:36AM Live 
X22.00001: Clusters and Surfaces in Reactive Atmospheres at Realistic Conditions: Beyond the Static, Monostructure Description Invited Speaker: Luca Ghiringhelli The processes occurring at surfaces play a critical role in the manufacture and performance of advanced materials, e.g., electronic, magnetic, and optical devices, sensors, and catalysts. A prerequisite for analyzing and understanding the electronic properties and the function of surfaces is detailed knowledge of the atomic structure, i.e., the surface composition and geometry under realistic gasphase conditions. The key quantity for studying the structure and function of surfaces/clusters in reactive atmospheres is the Gibbs free energy, as function of number of particles, pressure, and temperature. Here, I present a set of methods for the sampling of the configurational space of (nano)clusters and surfaces in reactive (e.g., O2, H2) atmosphere, in the canonical and grandcanonical ensembles, aiming at the unbiased determination of the phase diagrams as function of temperature and partial pressure of the reactive gas. 
Friday, March 19, 2021 8:36AM  8:48AM Live 
X22.00002: Dissipative dynamics in isolated quantum spin chains after a local quench Yantao Wu We provide numerical evidence that after a local quench in an isolated infinite quantum spin 
Friday, March 19, 2021 8:48AM  9:00AM Live 
X22.00003: LoopCluster Coupling and Algorithm for Classical Statistical Models Lei Zhang, Manon Michel, Eren Elci, Youjin Deng Potts spin systems play a fundamental role in statistical mechanics and quantum field theory, and can be studied within the spin, the FortuinKasteleyn (FK) bond or the qflow (loop) representation. We introduce a LoopCluster (LC) joint model of bondoccupation variables interacting with qflow variables, and formulate a LC algorithm that is found to be in the same dynamical universality as the celebrated SwendsenWang algorithm. This leads to a theoretical unification for all the representations, and numerically, one can apply the most efficient algorithm in one representation and measure physical quantities in others. Moreover, by using the LC scheme, we construct a hierarchy of geometric objects that contain as special cases the qflow clusters and the backbone of FK clusters, the exact values of whose fractal dimensions in two dimensions remain as an open question. Our work not only provides a unified framework and an efficient algorithm for the Potts model, but also brings new insights into rich geometric structures of the FK clusters. 
Friday, March 19, 2021 9:00AM  9:12AM Live 
X22.00004: Relevance in the Renormalization Group and in Information Theory Amit Gordon, Aditya Banerjee, Maciej KochJanusz, Zohar Ringel The analysis of complex physical systems hinges on ability to sift out the relevant degrees of freedom from among the many others. Though much hope is placed in machine learning, it also brings challenges, chief of which is interpretability. It is often unclear what relation, if any, the architecture and trainingdependent learned "relevant" features bear to standard objects of physical theory. 
Friday, March 19, 2021 9:12AM  9:24AM Live 
X22.00005: Local Pressure for Strongly Inhomogeneous states James Dufty, Jeffrey Wrighton, Kai Luo Continuum descriptions of complex classical and quantum systems increasingly are alternatives to firstprinciples manybody analyses. The macroscopic momentum balance equation originates in the underlying exact conservation law, with a precisely defined operator for the associated momentum flux. Its average in a local equilibrium ensemble provides the basis for a hydrodynamic description. A local pressure can be defined in terms of the trace of the local equilibrium average momentum flux, or alternatively as a thermodynamic pressure obtained from the grand potential for the local equilibrium ensemble. Both have the same global pressure but can differ locally. For uniform temperature (equilibrium), the momentum flux trace agrees with the local thermodynamic pressure even for strong density inhomogeneity, providing a connection to density functional methods for hydrodynamic applications. For nonuniform temperatures (local equilibrium) and strong inhomogeneities, no simple relationship exists among the different local pressure definitions. However, agreement can be restored by adding a suitable divergencefree contribution to the local equilibrium average momentum flux*. 
Friday, March 19, 2021 9:24AM  9:36AM Live 
X22.00006: Scaling of the RandomField Ising Model in Two Dimensions Nikolaos G Fytas, Argyro Mainou, Martin Weigel Being one of the simplest models of magnetic systems with quenched disorder, the randomfield Ising model shows surprisingly rich critical behavior. Only recently has it been possible with the help of largescale numerical simulations to shed some light on a range of fundamental questions in three and higher dimensions, such as universality, critical scaling and dimensional reduction. The twodimensional model 
Friday, March 19, 2021 9:36AM  9:48AM Not Participating 
X22.00007: TimeSplitting Numerical Simulator of Nonstandard GPEs and Applications Syrian Truong We aim to develop and release a timesplitting numerical simulator of noisy drivendissipative GrossPitaevskii equations (GPE), for use in general nonHermitian problems. Our solver correctly addresses crucial method differences that other available GPE solvers neglect, when incorporating complex potential/coefficient and added noise term components for nonstandard GPEs, such as when considering the timedependency of the solution density. This solver has applications to any area of research which would benefit from simulations of nonstandard GPEs, which include any of the following traits: complex Laplacian term coefficients, complex potentials, complex nonlinear term coefficients, coupled components, added noise terms. Examples include simulating dynamics involving (critical) exceptional point physics and modeling (noisy) interacting condensates, which are systems proposed as a basis for unconventional computing systems. Although previous research on hybrid polariton BoseEinstein condensate computing systems has shown promising analytical results of an advantage over traditional computing systems, because of the approximations/limitations of the methods utilized in those approaches, those results should be verified through numerical analysis. 
Friday, March 19, 2021 9:48AM  10:00AM Live 
X22.00008: Theory of NonInteracting Fermions and Bosons in the Canonical Ensemble Hatem Barghathi, Jiangyong Yu, Adrian G Del Maestro We present a selfcontained theory for the exact calculation of particle number counting statistics of noninteracting indistinguishable particles in the canonical ensemble. This general framework introduces the concept of auxiliary partition functions, and represents a unification of previous distinct approaches with many known results appearing as direct consequences of the developed mathematical structure. In addition, we introduce a general decomposition of the correlations between occupation numbers in terms of the occupation numbers of individual energy levels, that is valid for both nondegenerate and degenerate spectra. To demonstrate the applicability of the theory in the presence of degeneracy, we compute energy level correlations up to fourth order in a bosonic ring in the presence of a magnetic field. 
Friday, March 19, 2021 10:00AM  10:12AM Live 
X22.00009: RMT Spectral Distribution Crossovers in Random Spin Chains DEBOJYOTI KUNDU, Santosh Kumar, Subhra Sen Gupta We study spectral properties and spectralcrossovers between different random matrix ensembles (Poissonian, GOE, GUE) in correlated spin chain systems, in the presence of random magnetic fields, and scalar spinchirality term, as a function of competing Hamiltonian parameters. We have investigated these crossovers in the context of levelspacing distribution and levelspacing ratio distribution. Using interpolating functions between PoissoniantoGOE and GOEtoGUE, we have fitted the crossovers, to random matrix interpolating parameter ‘λ’. We find that once λ is properly scaled, the crossover behavior exhibits universality, in the sense that it becomes independent of lattice size in the large Hamiltonianmatrix dimension limit. 
Friday, March 19, 2021 10:12AM  10:24AM Live 
X22.00010: Trapping in Growing SelfAvoiding Walks: Numerical and Exact Results Alexander Klotz, Wyatt Hooper, Everett Sullivan Selfavoiding walks on lattices are used to model the statistics of polymer chains. Here we consider growing selfavoiding walks (GSAWs) on a lattice, which grow by taking their Nth step into a randomly chosen unoccupied site adjacent to the N1th step. It is known from simulations that on a square lattice, a GSAW will become trapped after a mean of 71 steps, but this is a purely empirical fact. We have extended the square lattice GSAW to include nearestneighbor attractive interactions, similar to those used to model polymers in poor solvents, which lead to a nonmonotonic trend in the mean trapping length. To gain additional insight into the statistics of GSAW trapping, we consider simplified cases of geometrically restricted lattices that are two to three sites wide. Using recursion relations and generating functions, we are able to derive exact expressions for parameters such as the mean trapping length, the asymptotic behavior of the trapping probability distribution, and the effect of nearestneighbor attraction, finding, for example, that walks on a restricted square lattice are trapped after a mean of exactly 17 steps. Our findings provide mathematical insight into a phenomenon that has been known only empirically since the 1980s. 
Friday, March 19, 2021 10:24AM  10:36AM Live 
X22.00011: "Temperature scaling" in quantum phase transitions with clusterupdate quantum Monte Carlo Yoshihiko Nonomura, Yusuke Tomita Advanced quantum Monte Carlo algorithms such as the loop algorithm [1] are based on the cluster update, and their relaxation has been considered too fast to apply the nonequilibrium relaxation (NER) method based on the powerlaw critical relaxation [2]. The present authors revealed that the critical cluster NER in classical spin systems is described by the stretchedexponential relaxation [36]. They generalized this procedure to the loop algorithm, and analyzed quantum phase transitions with the cluster NER [7]. Recently, the present authors proposed that the offcritical behaviors in classical spin systems can also be analyzed with the NER framework [8], and called this scheme as the "temperature scaling". In the present talk, we generalize this scheme to quantum phase transitions. As an example, we consider the Néeldimer quantum phase transition in the twodimensional S=1/2 antiferromagnetic Heisenberg model with columnar dimerization. 
Friday, March 19, 2021 10:36AM  10:48AM Live 
X22.00012: Density and other spectral properties of MuttalibBorodin ensembles and gammaensembles in Random Matrix Theory Kazi Alam, Swapnil Yadav, Khandker A Muttalib A simple method to calculate density, twopoint correlation function, and other statistical quantities of interest for a class of random matrix ensembles is presented. We reproduce some known results for wellstudied random matrix ensembles with varying potentials and twobody interaction. New results for spectral properties of the MuttalibBorodin ensemble and recently introduced gammaensemble were also obtained numerically for which no analytical method is available yet. 
Friday, March 19, 2021 10:48AM  11:00AM Live 
X22.00013: Generalized MuttalibBorodin ensembles, Laguerre βensembles and effective potentials Swapnil Yadav, Kazi Alam, Khandker A Muttalib, Dong Wang The eigenvalue density for Generalized MuttalibBorodin ensembles (also called γensembles) can be computed by solving equivalent equilibrium problem for MuttalibBorodin (MB) ensembles with γdependent effective potentials. Ideally, an exponent γinduced hardedge to softedge transition in eigenvalue density could describe a disorder induced metal to insulator transition in mesoscopic conductors. Such a transition in density has previously been produced only by especially designed nonmonotonic confining potentials of MB ensembles. We find that the effective potentials computed for a range of parameter of hardedge γ–ensembles with standard monotonic potentials show increasing nonmonotonic behavior near the origin as γ is decreased (or disorder is increased) systematically. While this nonmonotonicity is not sufficient to produce a hardedge to softedge transition in density in this toy model, it suggests that with appropriate combination of the additional interaction and the confining potential, such a transition can indeed occur. As a byproduct of the above calculations we also obtain the eigenvalue densities of Laguerre βensembles for any β>1. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2023 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700