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 GG07: V: Theory and Computation in Chemical Physics |
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Sponsoring Units: DCP Chair: Jingsong Zhang, University of California, Riverside Room: Virtual Room 7 |
Monday, March 20, 2023 12:30PM - 12:42PM |
GG07.00001: Real-Time TD-DFT Simulation of Secondary Electron Yields Under Focused Electron Beam Irradiation David B Lingerfelt, Jacek Jakowski, Panchapakesan Ganesh, Bobby G Sumpter Modern scanning transmission electron microscopy (STEM) techniques can utilize a variety of different modes of detection in the study of electronic and structural properties of thin materials. Signals from many commonly applied detection methods — e.g., electron energy loss spectra, which report on excitations induced in materials through inelastic scattering — are well understood from the theoretical perspective, and can nowadays be accurately calculated from first principles. In this presentation, we highlight new developments from our group towards the ab initio simulation of ionization processes (i.e., secondary electron generation) that occur under focused electron beam irradiation. Specifically, this work aims to expand our suite of time-dependent electronic structure theory methods for simulating beam-induced electronic excitations between bound states1 to also address transitions of material-bound electrons into unbound final states. Motivated by similar approaches for simulating photoelectron generation,2 a (real-time) TD-DFT method is put forth in which an idealized focused electron beam-like perturbation is applied to the system while absorbing boundary conditions are imposed to remove unbound secondary electrons. The electron density lost due to the perturbation is then related to the secondary electron yield. Results are presented for some prototypical conducting materials, which have been studied via STEM through secondary electron e-beam induced current measurements. |
Monday, March 20, 2023 12:42PM - 12:54PM |
GG07.00002: Detection of DNA Bases Using Single-Layer Ti3C2 MXene: Density Functional Theory Calculations Benjamin O Tayo, Michael Walkup, Sanjiv K Jha, Chinedu E Ekuma Electronic DNA sequencing using atomically thin 2D-based nanodevices has recently emerged as the next-generation of DNA sequencing technology. Recent molecular dynamics simulations showed that Ti3C2 has a great potential for detecting individual DNA bases. In this work, we employ first-principles techniques based on density functional theory (DFT) to quantify the electronic interactions of the four DNA nucleobases (adenine, thymine, guanine, and cytosine) with 2D Ti3C2. We performed calculations on two configurations of single-layer Ti3C2, namely, the 2D configuration, and the 1D (nanoribbon) configuration. Our results showed unique electronic structure changes of single-layer Ti3C2 induced due to adsorption of DNA nucleobases, demonstrating the potential of using Ti3C2 for electronic DNA nucleobase detection. |
Monday, March 20, 2023 12:54PM - 1:06PM |
GG07.00003: Uniaxial strain induced third-order Hall effect in graphene Hui Wang, Yue-Xin Huang, Shengyuan A Yang The transport phenomenon associated with the band geometric quantity has attracted a great deal of attention, and it has gone into the nonlinear terrain. Recently, the Berry connection polarizability has been discovered to be another intrinsic band geometric quantity that contributes to the third-order nonlinear Hall effect, which is prominent in nonmagnetic material with inversion symmetry or a twofold rotation. Based on the first-principles calculations, we find that graphene provides a promising platform for modulating third-order Hall response to applied electric field. By applying the uniaxial strain with breaking the 3-fold rotation symmetry, third-order Hall effect in graphene emerges and is estimated to be observable in experiments. This is attributed to the strain-induced anisotropy and tilt of the energy spectrum. Moreover, the sign of transverse conductivity is opposite for two different strain directions: along the zigzag and armchair directions. Through the strain engineering, our results indicate the possible nonlinear Hall effect in a large number of twodimensional materials with time-reversal symmetry and inversion symmetry. |
Monday, March 20, 2023 1:06PM - 1:18PM |
GG07.00004: The variational Gaussian approximation combined with high-order geometric integrators with applications to quantum tunneling and vibronic spectra Roya Moghaddasi Fereidani, Jiri Vanicek Among the single trajectory Gaussian-based methods for solving the time-dependent Schrödinger equation, the variational Gaussian approximation (VGA) [1,2] is the most accurate one. However, the equations of motion for the parameters of the Gaussian wavepacket require expectation values of the potential and its first two derivatives, making the method much more expensive than original Heller’s thawed Gaussian approximation (TGA) [3], which requires these potential energy properties only at the center of the wavepacket. To improve the efficiency of the VGA, we describe geometric integrators, which can achieve an arbitrary even order of convergence in the time step and are obtained by symmetrically composing the second-order symplectic integrator of Faou and Lubich [4]. We demonstrate that the high-order integrators can drastically speed up convergence compared to the second-order algorithm and, in contrast to the Runge-Kutta method, are time-reversible and conserve the norm exactly. To avoid making further approximations, we demonstrate the properties of the VGA and of the geometric integrators on several systems, in which the expectation values of the potential energy can be evaluated analytically. We show that the VGA, in contrast to the TGA, conserves energy exactly and takes into account tunneling at least qualitatively and, in calculation of vibronic spectra, it agrees better than the TGA and global harmonic approximation with benchmark exact quantum calculations. Finally, to show that the method is not restricted to low-dimensional systems, we also applied it to a nonseparable twenty-dimensional model of coupled Morse oscillators. |
Monday, March 20, 2023 1:18PM - 1:30PM |
GG07.00005: Polaritonic Ground and Excited State Energies on Superconducting Processors Mohammad H Hassan, Fabijan Pavosevic, Derek Wang, Johannes Flick In polaritonic chemistry, strong light-matter interactions between molecular matter and cavity photons can alter chemical reactions. While classical first-principles approaches exist to describe such systems, their complexity scales exponentially with system size. Quantum algorithms offer a potentially more efficient route toward simulating such systems. In this work, on IBM's superconducting quantum processors, we compute the ground- and excited-state properties of a polaritonic system: H2 in an optical cavity. To compute ground-state energies, we use the variational quantum eigensolver algorithm with a physically motivated and resource-efficient quantum electrodynamics unitary coupled cluster ansatz [1]. Then, we use the quantum electrodynamics equation-of-motion method to compute excited-state energies and transition dipole moments. By tuning the bond length and light-matter coupling strength, we generate polaritonic potential energy surfaces which can be used for quantum dynamics simulations of polaritonic systems. This work highlights the potential importance of quantum algorithms for polaritonic systems. |
Monday, March 20, 2023 1:30PM - 1:42PM |
GG07.00006: Structural Phase Transition in Bismuth Oxide due to Cooperative Pseudo Jahn Teller distortion Kelvin Dsouza, Daryoosh Vashaee Bismuth oxide is the base of several promising materials for various applications concerning the microelectronics and energy conversion industry. The present investigation aims to unveil the underlying reason for its phase transitions, e.g., δ→β→α, yet not completely understood, based on a combination of experimental and first principle studies. The calculations confirm that the orientations of the stable and metastable phases are attributed to the positions of lone pairs from the 6s2 orbitals of the Bi atoms. However, the structural relationship between the different phases of the crystal raises the more fundamental question of the underlying mechanism governing the phase transitions in this system. The electron localization function calculations predict the location of these lone pairs, and the crystal orbital hamiltonian population calculations confirm the bonding and antibonding between the orbitals. These results indicate that the observed phase transitions are due to the cooperative pseudo-Jahn-Teller distortion in the crystal originating from mixing the ground state Bi6s and excited Bi6p states. Therefore, we endorse the role of O2p states in stabilizing the lone pair activity, which leads to a pseudo-Jahn Teller distortion that cooperatively induces the phase transition. |
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