Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session W62: Computational Methods for Statistical Mechanics: Advances and Applications IIIFocus
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Sponsoring Units: DCOMP Chair: Mariia Karabin, Oak Ridge National Lab Room: Room 417 |
Thursday, March 9, 2023 3:00PM - 3:36PM |
W62.00001: Numerical and analytical methods for self-organizing disordered nanowires Invited Speaker: Francesco Caravelli There has been a lot of interest in nanoscale devices that can mimic some brain functionalities. In this talk, we discuss |
Thursday, March 9, 2023 3:36PM - 3:48PM Author not Attending |
W62.00002: From bulk descriptions to emergent interfaces Nirvana Caballero Controlling interfaces is highly relevant from a technological point of view. In ferroelectric materials, the energetically equivalent states of the polarization likely give rise to the existence of structures at the nanoscale in the form of interfaces (domain walls) which are widely used in sensing, actuation, nonlinear optics and information storage applications. Emergent structural and functional properties of these domain walls are widely studied for their potential integration as active nanoelectronic device components. However, their rich and complex behaviour makes them very difficult to describe theoretically and hence to predict and control. We address this problem by developing Ginzburg-Landau-type models which have the advantage of allowing us to study domain properties in combination with interface characteristics, and that can capture features of realistic realizations of interfaces. I will show how these models can be successfully employed to probe the effects of different experimental protocols over interfaces and domains and to develop new observables to characterize highly irregular interfaces. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W62.00003: Surrogate Models and Statistical Mechanics of Hexagonal Orderings in Delafossites Markus Eisenbach, Rinkle Juneja, Sinchul Yeom, Tomohiro Ichiba, Mina Yoon, Jaron T Krogel, Fernando A Reboredo Artificial ordered materials can be synthesized in laboratory settings. Of great interest is to identify layered materials where the in layer order appears spontaneously. One class of materials are PdCrO2 based delafossites where doping on the Pd plane could potentially change triangular ordering in the layer to a Kagome or honeycomb structure. We will explore the effect of chemical doping to control the change of this in plane ordering between honeycomb and Kagome patterns in delafossites of the form Pd1-x Ax CrO2 by generating surrogate models based on first principles calculations. The first principles calculations consider unbiased disorder realizations to capture the interactions inside the planes based on the chemical environment. These models form the basis for our Monte-Carlo simulations where we identify the transitions between the differently ordered states as a function of chemical composition as well as the transition temperatures for these hexagonal orders. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W62.00004: Ab initio kinetic models for the reactions of carbon dioxide with water under supercritical conditions Chu Li, Nore Stolte, Ding Pan Understanding aqueous carbon reactions at elevated pressure and temperature conditions is of great importance to the carbon transport in the deep Earth, which also greatly influences the carbon budget in near-Earth reservoirs. Here, we constructed the Markov States Models (MSMs) based on ab initio molecular dynamics (AIMD) simulations to study the reaction kinetics of carbon dioxide (CO2) in supercritical water in the bulk phase and under nanoconfinement. Our MSMs reveal that there are two distinct reaction paths for the formation of carbonate or bicarbonate ions. In the bulk solutions, CO2 tends to directly react with H2O or OH-, whereas under nanoconfinement the pyrocarbonate ion (C2O52-) is an important reaction intermediate. Interestingly, the CO2(aq) reactions are often mediated by rapid proton transfers along hydrogen bond wires, which are concerted in the bulk water, but stepwise under nanoconfinement. Our work provides a methodical and unbiased approach to study the reaction mechanism of CO2 in supercritical water at the atomistic scale, which has great implications for the deep carbon cycle. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W62.00005: Competition between Long- and Short-Range Order via Cluster Expansion and Machine Learned Interatomic Potentials Tzu-chen Liu, Nathan C Smith, Yi Xia, Christopher M Wolverton We calculate the phase stability in the Cr-Mo-W system with Density Functional Theory, Cluster Expansion (CE), and Moment Tensor Potentials (MTP) combined with Monte Carlo simulation. We find a surprising competition between the long-range order (LRO) present in the phase diagram and the short-range order (SRO) in the solid solutions. In the size-mismatched binary subsystems, Cr-W and Cr-Mo, the calculations reproduce the experimentally observed miscibility gap in both systems; however, SRO in the high-temperature disordered solid solutions are predicted to be ordering type. This apparent contradiction is explained by the coherency strain energies that are even larger than the mixing energies of the solid solutions. The phase-separating LRO is determined by the incoherent competition between phases, and is not subject to the coherency strain constraints. Hence, the energy of the random alloy is above the incoherent phase separation between the elements, but is below the coherent phase separation energy, explaining the predicted competition between LRO and SRO. The significant coherency strain energy provides an energetic penalty for clustering in the solid solution for systems with a large size mismatch, leading to the phenomenon of mechanically/incoherent clustering but chemically/coherent ordering. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W62.00006: Vibrational entropy of crystalline solids from covariance of atomic displacements Michael Widom, Yang Huang Understanding finite-temperature mechanical and dynamical properties of a material is essential for investigating its stability and phase behavior. The well-known harmonic approximation successfully predicts vibrational modes of harmonic systems yet fails when describing strongly anharmonic systems due to imaginary modes. Here we propose a method that overcomes mechanical instability of strongly anharmonic systems and is capable of predicting accurate vibrational entropy at finite temperature. In our method, we construct a covariance matrix by collecting pair correlations from molecular dynamic simulations and derive a relation between the covariance matrix and the vibrational entropy based on information entropy theory. We further obtain an effective force constant matrix in our approach, where harmonic approximation can be applied. Our approach is examined in both harmonic sytems (BCC Na and FCC Al) and anharmonic systems (BCC Ti). |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W62.00007: Examining the Rich Magnetic Phases of FeI2 with Monte Carlo Simulation Matthew S Wilson, Ying Wai Li, Kipton Barros, Xiaojian Bai, Martin P Mourigal, Cristian Batista The ferrous halide, FeI2, exhibits a rich variety of magnetic phases, which have not been fully understood despite decades of experimental1 and theoretical2 study. A common modeling strategy is to seek the simplest model that captures qualitative features, e.g., as observed from magnetization and neutron diffraction data. The magnetic dipoles of this system can be well modeled as Ising spins with both ferromagnetic and antiferromagnetic interactions on a triangular lattice. We use replica-exchange Monte Carlo simulations to map the magnetic phase diagram in temperature and external magnetic field, and report a number of exotic magnetic orderings. We find evidence for a 3Q magnetic structure that could relax into a skyrmion lattice upon softening the easy-axis anisotropy, and a “floating” phase where the ordering wave vectors move continuously. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W62.00008: Kinetic control of competing nuclei in a dimer lattice-gas model Dipanjan Mandal, David Quigley Nucleation is a key step in the synthesis of new material from a solution of its components. Competition of clusters with different structures is often observed in nature. Free energy calculations can show which structure is most stable at each cluster size, favouring the stable bulk structure as the cluster size approaches the thermodynamic limit. Nevertheless, significant populations of large and very long lived metastable post-critical nuclei are often observed in experiments. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W62.00009: Mitigating the sign problem with Permutation Matrix Representation quantum Monte Carlo Itay Hen The Permutation Matrix Representation quantum Monte Carlo algorithm [Gupta, Albash and Hen, J. Stat. Mech. (2020) 073105] is a parameter-free Trotter error-free QMC technique designed to tackle a very broad range of physical models within a single unifying framework. In this approach, configurations correspond to closed walks on the Hamiltonian matrix graph. I will demonstrate how this technique can be used to mitigate the sign problem in a variety of quantum many-body models. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W62.00010: Strain-induced two-step phase transition and polar-antipolar mode coupling stabilize robust ferroelectricity in thin-film hafnia songsong zhou, Jiahao Zhang, Andrew M Rappe Hafnia attracts considerable research interest due to its compatibility with current silicon technologies and its robust ferroelectricity in the thinnest film, which make it a promising candidate for next generation devices to overcome many issues of devices based on perovskite ferroelectrics. However, the origin of this robust ferroelectricity and the ferroelectric phase transition mechanism is still elusive. Here, we prove that the robust ferroelectricity arises from a unique two-step antipolar-ferroelectric phase transition, which is induced by tensile strain and strong polar-antipolar mode coupling. The antipolar mode instability could be induced by tensile strain and thus the first-step phase transition to an antipolar phase could be activated. When the amplitude of antipolar mode is above a threshold, the secondary ferroelectric phase transition occurs due to the cooperative coupling between antipolar and polar mode. Since the antipolar mode is not susceptible to depolarization, the spontaneous antipolar displacement, through the cooperative polar-antipolar mode coupling, could stabilizes the polarization against depolarization effect. We demonstrate that this polar-antipolar coupling is strong enough to offset even the unscreened depolarization field and stabilize the polarization even in the thinnest film. Our results demonstrate that the strain and polar-antipolar coupling are the origins of robust ferroelectricity in hafnia. This finding of strain induced phase transition could also explain the reverse size effect in hafnia and the cooperative mode coupling effect provides a new mechanism against depolarization other than conventional improper ferroelectricity. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W62.00011: A Computational Investigation of the Barium Titanate Surface Interactions with Tert-Butylphosphonic Acid Jessica Marvin, Erina Iwasa, Cedar Turek, Nilay Pangrekar, Whitney C Fowler, Renee M Van Ginhoven, Todd Monson, James Nicholson Barium Titanate (BTO) is a ferroelectric material that has been widely researched and used in capacitor applications because of its large dielectric constant. To expand its range of applications, BTO has been successfully incorporated into composite nanoparticle matrices while still maintaining a high dielectric constant. A key step discovered in this manufacturing process is to coat BTO nanoparticles with phosphonic acid ligands to prevent particle aggregation and maximize the composite's dielectric constant. However, phosphonic acid ligands have been shown to interact with and modify metal oxide nanoparticle surfaces, potentially negatively impacting dielectric properties. In this presentation, we use density functional theory (DFT) calculations to report how tert-butylphosphonic acid bonds to the TiO2-terminated surface of bulk BTO. We present the binding energy associated with various tert-butylphosphonic acid/barium titanate interactions to determine the favorable binding modes, providing valuable insight into optimizing ferroelectric properties of the BTO composite material. |
Thursday, March 9, 2023 5:36PM - 5:48PM Author not Attending |
W62.00012: Theory of excitonic topological order in imbalanced electron-hole bilayers Rui Wang Correlation and frustration play essential roles in physics, which give rise to a variety of exotic quantum phases, e.g., the quantum spin-liquids. On the other hand, boson condensation is known to generate quantum state with macroscopic coherence such as superfluid. In semiconductors, it is well known that electrons and holes can form bosonic pairs, termed excitons, which can condense and form excitonic insulators. Then, a key question of great interest is that whether excitons can always condense at zero temperature, and is it possible for quantum spin-liquid like physics to emerge in excitonic systems under certain circumstances? We show that correlated electron-hole bilayers with density imbalance could support an excitonic topological order (ETO) in the phase diagram, which is a time-reversal breaking topological order with fractionalized excitations, akin to the fractional quantum Hall states. At microscopic level, the density imbalance leads to excess particles competing with the formed excitons, resulting in large degeneracy of exciton configurations, i.e., the frustration. The frustration is manifested in momentum space as a moat-like band (similar to flat band). The interacting excitons on moat band cannot condense. Instead, we show that the ETO emerges in certain parameter range with lower energy than all known boson condensation states. The ETO exhibits edge states consisting of a pair of chiral electron and hole channel. It well explains the recent experiments in InAs/GaSb quantum wells, in terms of the observed excitonic bulk gap under strong electron-hole density imbalance and the edge transport under both zero and high magnetic fields. |
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