Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session Q07: Computational PhysicsRecordings Available
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Sponsoring Units: DCOMP GFB Chair: Felipe J. Llanes-Estrada, Univ Complutense Room: Salon 4 |
Monday, April 11, 2022 10:45AM - 10:57AM |
Q07.00001: Intrinsically Localized Lattice Vibrations in Crystalline Lattices Benjamin A Agyare The formation of Intrinsically Localized Modes (ILMs) for a pair of harmonic phonons along the direction [111] of the Sodium Iodide (NaI) crystalline lattice is examined. The tendency for ILMs to form at a certain center-of-mass momentum q and corresponding relative momentum vector k is attributed to the van-Hove singularities condition in the non-interaction two-phonon density of states continuum. It is observed that, as q converges to the high-symmetry point L=q (π, π, π) of the Brillouin zone, the relative momentum vector k remains invariant at k(π/2, π/2, π/2) for a certain threshold value of q, and coalesces at the upper-edge of the two-phonon density of states spectrum with high degeneracy in the two-phonon critical energy. It can be concluded that the excitation spectra of the pairs of harmonic phonon excitations become energetically degenerate past the threshold q value towards L at the invariant vector k, announcing the strong presence of ILMs. The calculated ILMs is observed at a critical energy of 20.0 meV for a nearest neighbor and next-nearest neighbor spring coupling constants ratio of 0.598. Reports of Inelastic Neutron Scattering experiments have identified one-phonon breather excitations energy of 10.2 meV at elevated temperatures of 555 K. The formation of ILMs, or multi-phonon bound states, is expected to arise as a result of the anharmonic interactions that lift these degeneracies to enhance the formation of ILMs. |
Monday, April 11, 2022 10:57AM - 11:09AM |
Q07.00002: Quanta in Quasicrystals, with Dual Harmonics Antony J Bourdillon Relevance: Condensed matter often spawned new general physics (Fermi level, fermions, bosons etc.) Bragg’s law depends on harmony in integral order. Diffraction in Quasicrystals requires simultaneous harmony between periodic probes and geometric series diffraction. Notice that quanta are confined by harmonic states (Schrödinger’s eigenstates). Fact: Quasicrystal diffraction [1] is in irrational, aperiodic and geometric order, with icosahedral point group symmetry. The indices due to 4-D hierarchic icosahedra are separable into natural numbers with irrational residues. The latter cause metric stretch that enables commensurate harmony in both linear and geometric space. The stretch causes translational symmetry, both long range and short, in the quasi-Bloch-wave probe. Numerical quasi-structure-factor simulations exactly match both Fibonacci series analysis and verification by quasi-lattice parameter measurement. Quasicrystals teach how the momentum quantization results from the dual harmonics. Corollary: Dimensions should not be multiplied without necessity; nor fields; nor quanta (of gravity). [1] Journal of Modern Physics, (2021) 12 1618-1632. doi: 10.4236/jmp.2021.1212096 |
Monday, April 11, 2022 11:09AM - 11:21AM |
Q07.00003: Efficiency and stability of numerical force-free electrodynamics using pseudo-spectral methods. Cristobal Armaza, Saul Teukolsky, Lawrence E Kidder Prior to merger, the magnetospheric interaction of a neutron star with its companion is expected to produce electromagnetic radiation. This emission--yet to be detected--can provide key information about the source, not accurately obtainable with gravitational radiation alone. In this context, force-free electrodynamics (FFE) has been proposed as a valuable simplification for describing magnetospheric interactions of merging neutron stars. In this talk, we will present FFE simulations using pseudo-spectral methods, putting emphasis on finding stable and efficient methods of solving the FFE equations. Applications will be also discussed. |
Monday, April 11, 2022 11:21AM - 11:33AM |
Q07.00004: Multipole Moments of the Common Horizons in a Binary-black-hole Simulation Yitian Chen, Prayush Kumar, Neev Khera, Nils Deppe, Saul Teukolsky The final state of a binary-black-hole system is a Kerr black hole. However, the black hole immediately after the merger is highly distorted. To analyze the evolution of this distortion, we construct a set of spatially gauge-invariant horizon multipole moments using the spectral Einstein code. We find that these moments are well described by the fundamental tones of spin-weight-2 quasinormal modes at late times. We see that each moment is comprised of several quasinormal modes instead of only one mode. We also explore the possible quasinormal description of these moments at early times near the merger. |
Monday, April 11, 2022 11:33AM - 11:45AM |
Q07.00005: Computational studies of current driven instabilites in a tokamak plasma Jervis R Mendonca, Joydeep Ghosh, Rakesh Tanna, Abhijit Sen The system of nonlinear coupled equations in magnetohydrodynamics (MHD) is an extremely challenging area of research, due in part to their non-self-adjoint nature. This necessity has led to the development of numerical techniques for the accurate solution of these equations, particularly applied to the laboratory plasma devices such as tokamaks. Tokamak is one of the most successful candidates for the development of a fusion reactor. This work focuses on simulation of current driven instabilities occurring in tokamaks, particularly the tearing and kink modes, whose nonlinear evolution is not yet well understood and has a significant role in the operation and eventual success of tokamaks as reactors. These simulations are carried out using the CUTIE code [1] implementing novel computational techniques. Among these chiefly we have a modified TDMA method which improves the accuracy of our nonlinear calculations, nonlinearization method. We also describe the resolvent method, which is an eigenvalue method to quickly determine linear growth rates and frequencies, which serve as a check on the time evolution results. The simulation results are compared with experimental observations in ADITYA-U tokamak [2, 3, 4] for a better understanding of the tearing-mode behavior. |
Monday, April 11, 2022 11:45AM - 11:57AM |
Q07.00006: Understanding Weakly Interacting van der Waals Fermi Systems via Renormalization Group Theory Sushant K Behera Weak-coupling phenomena of the two-dimensional Hubbard model is gaining momentum as a new interesting research field due to its extraordinarily rich behavior as a function of the carrier density and model parameters. Salmhofer [{\it Commun. Math. Phys}. \textbf{194}, 249 (1998);{\it Phys. Rev. Lett}. {\bf 87}, 187004 (2001)] developed a new renormalization-group method for interacting Fermi systems and Metzner [{\it Phys. Rev. B} {\bf 61}, 7364 (2000);{\it Phys. Rev. Lett}. {\bf 85}, 5162 (2000)] implemented this renormalization group analysis of the two-dimensional Hubbard model. In this work, we demonstrate the spin-wave dependent susceptibility behavior of model graphene-phosphorene van der Waals heterostructure in the framework of renormalization group approach. We implement signlet vertex response function for the weakly interacting van der Waals Fermi system with nearest-neighbor hopping amplitudes [{\it J. Phys.: Condens. Matter} {\bf 33}, 335604 (2021)]. This analytical approach is further correlated with {\it ab initio} simulation results and extended for spin-wave dependent susceptibility behavior with possible experimental protocols. We present the resulting compressibility and phase diagram in the vicinity of half-filling, and also results for the density dependence of the critical energy scale. |
Monday, April 11, 2022 11:57AM - 12:09PM |
Q07.00007: Quantum entanglement in the bilinear-biquadratic model for iron-based superconductors LEONARDO S LIMA Recently there has been a renewed interest in biquadratic exchange interactions in recently discovered two-dimensional magnets. In a general way, biquadratic interactions are present in spin-1 magnets being known as to favor nematic ordering.[1-10] In this work we study quantum correlation in the spin-1 two-dimensional Heisenberg model on square lattice with biquadratic interactions and the next-nearest neighboring interaction or bilinear-biquadratic (BBQ) model is investigated. The calculations were performed for the model in the quadrupolar phases using SU(3) flavor-wave theory. We calculate the von Neumann entropy as a function of the biquadratic couplings, Jbq1, Jbq2 and next-nearest neighboring exchange interaction of the lattice with aim to very the effect of different phase transitions as the phase transition Néel-quadrupolar on quantum entanglement. |
Monday, April 11, 2022 12:09PM - 12:21PM |
Q07.00008: Calculations of S--P transition energies and oscillator strengths in few-electron atoms and ions Sergiy Bubin, Saeed Nasiri, Ludwik Adamowicz First-principle calculations of transition energies in atoms with accuracy that matches high-resolution spectroscopic measurements is a challenging task. For few-electron atoms (n=2-6), however, this can be done within the framework of the variational method augmented with the use of all-particle explicitly correlated Gaussians (ECGs) and the perturbation theory for treatment of leading relativistic and quantum electrodynamics effects. In this talk I will consider several low-lying S and P states of lithium, beryllium, and carbon ion and demonstrate the current capabilities of the approach. I will also talk about the calculations of dipole moments and oscillator strengths corresponding to S--P transitions. |
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