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 L25: Assigning Structures to Spectra Using Density Functional Theory: Method and Applications IIIFocus Live
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Sponsoring Units: DCP Chair: Benjamin Janesko, Texas Christian Univ; Giovanni Scalmani, Gaussian, Inc. |
Wednesday, March 17, 2021 8:00AM - 8:36AM Live |
L25.00001: Electronic and molecular structural dependence of metal oxide cluster reactions with water Invited Speaker: Caroline Jarrold The molecular scale interactions that govern the catalytically-driven hydrogen evolution reaction from water can be probed by combining anion photoelectron spectroscopic probes of metal oxide cluster models of heterogeneous catalysts with experimental cluster + water reactivity studies and computational treatment. The application of this multi-prong approach to group 6 transition metal oxides will be described, as well as the extension to near-neighbor heterometallic (group 5/group 6; group 6/group 7) oxide cluster systems. The importance of asymmetric oxidation states and oxophilicities emerge from these studies. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L25.00002: Modeling liquid water by climbing up Jacob's ladder in density functional theory facilitated by deep neural network Chunyi Zhang, Mohan Chen, Linfeng Zhang, Michael L Klein, John Perdew, Xifan Wu Climbing Jacob's ladder up to the fourth rung is essential in order to build a more accurate model of water within the framework of density functional theory (DFT). Also, ideally due to the light-mass of the protons, quantum effects need to be considered simultaneously via Feynman's path integral technique. In this work, we model the structural and dynamic properties of liquid water by ab inito molecular dynamics (MD) based on the hybrid functional (SCAN0) of the recently developed SCAN meta-GGA functional. Furthermore, in order to carry out larger and longer MD simulations to be able to predict the properties of liquid water with the same accuracy as DFT, we employ Deep Neural Network models based on both DeePMD and Deep Wannier. Specifically, we are able to predict not only thermodynamic properties but also dynamic properties (e.g., the diffusivity), and the electronic response (e.g., dielectric constant and infra spectroscopy). The results indicate that the structural, electronic, and dynamic properties of liquid water are systematically improved due to the mitigated self-interaction error and inclusion of nuclear quantum effect in the modeling. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L25.00003: First principles simulations of the liquid-liquid transition in water using deep neural networks Thomas Edward Gartner, Linfeng Zhang, Pablo Piaggi, Roberto Car, Athanassios Panagiotopoulos, Pablo Gaston Debenedetti A metastable liquid-liquid transition (LLT) has been observed in simulations of several molecular models of water, but experimental evidence for or against this phenomenon remains elusive due to rapid ice nucleation under supercooled conditions. As such, attempting to definitively identify water's LLT is an active area of study in simulations and experiments. In this work, we used the Deep Potential Molecular Dynamics (DPMD) technique to generate an ab initio deep neural network (DNN) model for water based on density functional theory calculations with the SCAN exchange correlation functional. We then performed enhanced-sampling molecular simulations in the multithermal-multibaric ensemble to obtain the thermophysical properties of the DNN model over a wide range of temperatures and pressures. The simulation results were suggestive of the existence of a liquid-liquid critical point, and we used a two-state equation of state to estimate its location. These results provide computational evidence, completely from first principles, that is suggestive of the existence of the LLT in real water. We also discuss our ongoing work to apply free energy methods to definitely establish liquid-liquid coexistence using this model and solidify the computational evidence for this phenomenon. |
Wednesday, March 17, 2021 9:00AM - 9:36AM Live |
L25.00004: Modeling electron detachment with efficient electronic structure methods Invited Speaker: Hrant Hratchian Metal oxide clusters can serve as molecular models of surface defect sites and can be probed using well established experimental techniques such as photoelectron spectroscopy. However, definitive spectral assignments often require corroborating computational simulations. Such calculations can be significantly complicated by the presence of unpaired and strongly correlated electrons and can further challenge interpretations of computational results. This talk will describe our lab's recent studies of these systems and our efforts to develop new efficient methods for treating the complicated electronic structures often encountered in these systems, with a focus on advances impacting collaborations with experimentalists. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L25.00005: Time-reversible high-order integrators for the nonlinear time-dependent Schrödinger equation: Application to local control theory Julien Roulet, Jiri Vanicek The explicit split-operator algorithm (ESOA) has been extensively used for solving linear and nonlinear time-dependent Schrödinger equations (NLTDSEs).1 When applied to the Gross-Pitaevskii equation, the method remains time-reversible, norm-preserving, and retains its second-order accuracy in the time step.2 However, this algorithm is not suitable for all types of NLTDSE. Indeed, we demonstrate that local control theory, a technique for the quantum control of a molecular state, translates into a NLTDSE with a more general nonlinearity, for which the ESOA loses time reversibility and has only first-order accuracy, becoming very inefficient. To overcome these issues, we present high-order integrators for general NLTDSEs which preserve the geometric properties3 of the exact flow and are more efficient than the ESOA. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L25.00006: Structural Anharmonicity Provides a New Prospective of Vibrational Frequency Shifts in Ferroelectric and Antiferroelectric Materials Sydney N Lavan, Cathleen A Saraza, Kanwar Bhular, Sardou Sabeyo-Yonta, Adedayo M Sanni, Aaron S Rury There remain fundamental gaps in understanding how the microscopic electrostatics of hydrogen-bonded antiferroelectric molecular crystalline materials, such as 2-trifluoromethylbenzimidazole (TFMBI), control the macroscopic properties essential for their application in light generation, photovoltaic conversion of solar energy and electrostatic energy storage technologies. To determine if molecular vibrations can assess the microscopic electrostatics we conducted temperature-dependent Raman measurements. We find vibrational peaks shift to higher frequencies across different regions of the spectra. We first concluded the vibrational Stark effect is not an explanation. With DFT and a theoretical model of anharmonic contributions to vibrational frequencies, we assessed whether structural anharmonicity could explain the peak shifts we observed. We conclude the peak shifts likely results from thermally driven changes to the average occupation of other lower frequency intermolecular vibrations interacting with the Raman-active ring distortion vibrations of TFMBI. Furthermore, we are actively investigating methyl-benzimidazole (MBI), a ferroelectric material, where we will decipher if vibrational probes report the microscopic electrostatic drivers of the macroscopic properties. |
Wednesday, March 17, 2021 10:00AM - 10:36AM Live |
L25.00007: Manipulating spin and electrostatic effects in organic semiconductors Invited Speaker: David Beljonne Spin is expected to be a good quantum number in organic semiconductors where spin mixing effects associated e.g. to spin-orbit coupling are weak. In that respect, the formation of triplet excitations by electron-hole recombination in electroluminescent or photovoltaic devices ususally leads to light, current or voltage losses. In the first part of the talk, we will present a very recent combined experimental-theoretical work demonstrating that recombination of charge-transfer triplet excitations into localized triplets, acting as a sink for charge photogeneration, can be avoided by properly designing donor and acceptor molecules in order to favor hybridization or configurational mixing in the excited state. We will further demonstrate that it is possible to control triplet dynamics by coupling organic molecules to lanthanide-doped inorganic insulating nanoparticles through spin-exchange and charge-transfer interactions that turn the dark triplets into bright states. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L25.00008: Probing the unpaired Fe spins across the spin crossover of [Fe(L1)(bipy)]n coordination polymer by X-ray photoemission spectroscopy Thilini Ekanayaka, Hannah Kurz, Ashley S. Dale, Guanhua Hao, Aaron Mosey, Esha Mishra, Alpha N'Diaye, Ruihua Cheng, Birgit Weber, Peter A Dowben The spin crossover (SCO) phenomenon occurs in 3d transition metal compounds and is typically a temperature-induced transition of diamagnetic low spin (LS) state to paramagnetic high spin (HS) state. Intermolecular cooperative effects can be seen in the spin crossover transition which results a thermal hysteresis. The steric hindrance can result in thermal stabilization and can affect the spin transition temperature. This can also result in a mixed spin state for a given temperature. This bistability of these SCO molecules is important in implementing a spin crossover complex into a molecular device. In this study the spin-crossover coordination polymer [Fe(L1)(bipy)]n (where L is a N2O22− coordinating Schiff base-like ligand bearing a phenazine fluorophore and bipy = 4,4′-bipyridine), which exhibits a wide thermal hysteresis, above room temperature has been studied using different methods. The spin state transition temperatures obtained from XAS and XPS differ from temperature determined from magnetometry. This suggests that XAS and XPS may perturb the bistability of the spin crossover system or that the surface of a [Fe(L1)(bipy)]n crystal differs from the bulk. |
Wednesday, March 17, 2021 10:48AM - 11:00AM Not Participating |
L25.00009: Evaporation of water nanodroplets: does size matter? Luis Ruiz Pestana, Teresa Head-Gordon Understanding the wetting behavior and evaporation kinetics of droplets on solid substrates is central to many engineering and nanotechnological applications such as nanofabrication or spray cooling of electronics. While a broad range of continuum models exist to predict the evaporation of macroscale droplets, a similar level of understanding is lacking at the nanoscale, where many of the continuum assumptions break down and experimental systems become very hard to probe. Here, we use molecular dynamics to investigate the evaporation kinetics of water nanodroplets on heated substrates with different hydrophobicity. We find that all water nanodroplets follow a previously unidentified mode of evaporation characterized by large isovolumetric fluctuations. In contrast to diffusion-limited models, the evaporation rate of hydrophilic nanodroplets decays exponentially with the volume, and hydrophobic droplets follow stretched exponential kinetics. Our results show that the lifetime of the nanodroplets, which also disagrees with continuum predictions, strongly correlates with the time that takes the droplets to thermalize with the substrate, with hydrophobic droplets resulting in longer lifetimes. Interestingly, all droplets exhibit a non-uniform evaporative flux. |
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