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 S60: Electrochemical Interface I: Electrified InterfacesFocus
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Sponsoring Units: DCOMP Chair: Marivi Fernandez-Serra, Stony Brook University (SUNY) Room: Room 419 |
Thursday, March 9, 2023 8:00AM - 8:36AM |
S60.00001: Voltage-Dependent Dynamics and Surface-Specific IR Spectra of Water at Gold Electrodes from Deep Neural Network-Assisted Ab Initio Calculations Invited Speaker: Zachary Goldsmith Electrode-liquid interfaces under voltage biases demonstrate unique properties that govern their many energy conversion applications. Mean-field models and classical simulations of the electrical double layer (EDL) cannot describe molecular-level polarization or reactivity, necessitating controlled-potential density functional theory calculations to investigate such systems. Born-Oppenheimer ab initio molecular dynamics (AIMD) calculations of electrified Au(111) slabs interfaced with multiple monolayers of liquid water were performed using a hybrid explicit-implicit solvent approach. Fixed excess charges were localized on the Au slab and electrode potentials were computed on the fly to determine the system’s differential capacitance. The effects of modest positive and negative voltages on the structure, dynamics, and hydrogen bonding properties of interfacial water were elucidated and compared to available experiments. Additionally, the molecular dipoles of the water subsystem were computed at thousands of AIMD snapshots and further interpolated at each voltage using deep neural networks (DNNs). From these dipoles, the IR spectra specific to the interfacial water molecules versus applied voltage were obtained in good agreement with surface-enhanced IR absorption experiments. This work provides a framework for investigating species in the EDL and demonstrates the utility of machine learning for interrogating surface-specific vibrational spectroscopies of chemical species. |
Thursday, March 9, 2023 8:36AM - 9:12AM |
S60.00002: Invited Talk: Pablo OrdejonDFT and QM/MM simulations of electrified interfaces using Non-Equillibrium Green's Functions Invited Speaker: Pablo Ordejon Albeit water is the most common and thus most studied solvent, understanding its structure and properties at the surface of materials is still an open problem. Molecular modeling emerges as way to investigate critical technological electrochemical processes involved in developing batteries, fuel cells, anti-corrosion coatings, and many others in which water interacts with metallic, often electrified, surfaces. The latter can be addressed by using the non-equilibrium Green’s functions (NEGF) method, allowing us to consider the effect of the potential applied to the electrodes. Nonetheless, the typical size of the systems required to include a realistic number of water molecules and the time scale one needs to reach to obtain an accurate representation of these processes is prohibitive in computational cost. To tackle that problem, we have used a quantum mechanics/molecular mechanics (QM/MM) approach coupled to the NEGF method as implemented in the SIESTA package to investigate the metal-water interaction, providing a good balance between accuracy and computational cost. We validated our results against full QM calculations and analyzed the performance to evince the gain in using the QM/MM approach, showing that such a method emerges as a viable way of studying way larger systems compared to those currently used to investigate the dynamics of electrified metal-water interfaces. Our approach allows us to study the dynamics of liquid water in contact with electrified surfaces, reaching significantly longer simulations for systems containing hundreds of water molecules, while fully accounting for the electrode’s potential.
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Thursday, March 9, 2023 9:12AM - 9:24AM Author not Attending |
S60.00003: Anomalous perpendicular dielectric response of nanometer-thin water films Jon Zubeltzu, Emilio Artacho, Marivi Fernandez-Serra The perpendicular dielectric response of a one nm-thin water film was experimentally found to be surprisingly low [Fumagalli et al, Science 360, 1339 (2018)], with a relative dielectric constant of 2.1. There had been predictions of such an effect from simulations [e.g. C Zhang, F Gygi, G Galli, J. Phys. Chem. Lett. 4, 2477 (2013)], and further simulations after the experiments corroborated them [e.g. G. Monet et al,Phys. Rev. Lett. 126, 216001 (2021)]. The problem is, however, far from understood, since the simulations describe a mostly (or even uniquely) orientational response of the water molecules, while the experimental response seems to be mostly electronic (1.8 is the bulk value of the high-frequency relative dielectric constant). Using molecular-dynamics simulations of such a water film over long trajectories obtained from a TIP4P/2005 model, the dielectric response for the model is compared with the one obtained using density-functional theory calculations sampling the same trajectory, both using explicit dipole versus applied field calculations. With the same technique, the high-frequency response is also calculated for the film. The results are quite revealing and offer a better understanding of this anomalous behaviour. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S60.00004: Lower dielectric constant in nano-confined water: Interpreting anisotropy in confinement Youngji Jeong, Chang Yun Son Interface intrinsically breaks isotropy. Systems with confinement thus experiences different environment from isotropic systems which results in unusual dynamic properties. With growing interest in confined systems, lower dielectric constant of confined water is considered as one of the significant problems yet to be fully understood. Experiments and simulations verified that as the extent of confinement in water increases, the dielectric constant decreases. It is commonly thought that water molecules are electrostatically affected by surface of the confinement, forming specific structures and exhibiting distinctive dynamics. Examining the surface induced reduction, we conducted molecular dynamics simulation designed to produce different dielectric properties of confining walls. Interestingly, reduction of dielectric constant calculated from totally different dielectric conditions was almost identical. On the other hand, freeing surface fluctuation which was restricted by rigid surface recovers dielectric property to a certain extent. Longer correlation of dipole is also likely to responsible, as we investigated universal reduction in fluctuation of local polarization. From this study, we expect to explain the abnormal properties resulted from the anisotropy in more physical and concrete words. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S60.00005: Efficient calculation of the mean inner potential of solids using density-functional theory Oswaldo Dieguez, Avi Auslender, Amit Kohn The mean inner potential of a solid is the average over a unit cell of the Coulomb potential due to its charges. This magnitude is of relevance, for example, in transmission electron microscopy imaging and holography. It has been computed in the past for a few materials with density-functional theory, typically using all-electron codes. In this work we present a recipe to do so using files produced by a standard projected-augmented wave code (VASP). We have use this method to asess the agreement with experiment regarding the values of the mean inner potential of alumina [1] and graphite [2] in the past. In this talk I will report how we recently exploited its flexibility to understand how trends in the value of the mean inner potential change, for example, depending on composition and surface orientation of elemental crystals. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S60.00006: Electrified electrode-electrolyte interfaces from first principles Arihant Bhandari, Chao Peng, Jacek Dziedzic, Lucian Anton, John R Owen, Denis Kramer, Chris-Kriton Skylaris Reactions occurring at the electrochemical interfaces under applied potential govern the functioning and performance of devices for energy conversion and storage. To describe this phenomena at the atomic scale, we have developed a method for performing density functional theory (DFT) calculations in a grand canonical ensemble under potential control [J. Chem. Phys., 2021, 155, 024114]. The charge developed on the electrode is neutralized by a build up of counter charge in the electrolyte, which is represented via Poisson-Boltzmann theory in a grand canonical ensemble [J. Chem. Phys., 2020, 153, 124101]. The method works in both fully periodic and open boundary conditions [J. Phys. Chem. C, 2020, 124, 7860], and has been implemented in the ONETEP program [J. Chem. Phys., 2020, 152, 174111] which has a linear-scaling computational cost with the number of atoms. The model parameters have been calibrated with respect to reduction potential of standard electrodes and activity coefficient of electrolytes. The model has been applied to study the differential capacitance of graphene based electrodes in supercapacitor applications, and lithium nucleation on graphite anode in Li-ion batteries [J. Mater. Chem. A, 2022, 10, 11426]. The predictions from the model agree well with experiments. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S60.00007: Vibrational properties of water-metal interfaces under a bias potential Luana Pedroza, Graciele Arvelos The interest in renewable sources of energy has demanded a deeper understanding of the electrochemical process since it is one of the pillars of green energy sources. Consequently, first principles computer simulations, notably Density Functional Theory (DFT) ones, have provided crucial insights into the molecular and electronic structure of water-metal interfaces, dealing with charge and energy transfer reactions, adsorption, and heterogeneous catalysis. Despite these recent developments, the atomistic description of the structural and vibrational properties of the water-metal interface under an applied bias potential is still a challenge. Furthermore, experimental results showing the potential-dependent structure of the interfacial water have motivated first-principle calculations studies of hydrogen bond, and water-metal interaction under an external bias potential. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S60.00008: Learning Solvation: The Transition from Machine Learned Potentials of Bulk Solvent to Aqueous Solution Alec Wills, Marivi Fernandez-Serra, Luana Pedroza, Marcio S Gomes-Filho Due to its ubiquity and importance in daily life, highly accurate simulations of liquid water are critical to understand a variety of phenomena. With the onset and fast spread of machine learning methods across disciplines, development of neural network force fields that can capture the desired accuracy with reasonable computational efficiency is possible. Critically, neural networks can learn dynamics of ab initio simulations using high accuracy exchange-correlation function, allowing ab initio accuracy of simulations on a timescale not feasible for true ab initio methods. Recent work has demonstrated the efficacy of such methods when learning bulk structure and dynamics during simulation, but work remains to extrapolate these methods towards accurately simulating salts in solution in the dilute limit. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S60.00009: Origin of the dielectric decrement of salt water Chunyi Zhang, Shuwen Yue, Athanassios Panagiotopoulos, Michael L Klein, Xifan Wu The dielectric constant is one of the most important properties of salt water, which determines the Coulomb interactions between the solution components and therefore regulates the microstructures and the physicochemical properties of the solution. Since the last century, it has been widely reported in experiments that the dielectric constant of salt solutions decreases nonlinearly with increasing solute concentration, a phenomenon called dielectric decrement. In this work, we study the dielectric decrement using the advanced deep potential long range (DPLR) method, which enables efficient ab initio-level simulations. Moreover, DPLR includes long-range electrostatic interactions explicitly, which is essential for the correct description of long-range dipole-dipole interactions. The computed dielectric constant agrees well with experimental data. The detailed analyses indicate that the dielectric decrement is mostly due to the loss of correlation between water molecular dipoles, which is caused by ions' disruption to the tetrahedral hydrogen-bond network of water. The anti-correlation between water molecular dipoles in the ionic first solvation shells (FSSs) contributes to a steep and linear drop in the correlation factor. Whereas the nonlinear decrement originates from the reduced cross-dipolar correlation between water molecules within ionic FSSs with that outside the FSSs. Surprisingly, the dipolar correlation among water molecules outside ionic FSSs have a negligible effect on the dielectric decrement. |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S60.00010: Voltage-driven molecular catalysis of electrochemical reactions Guoxiang Hu, Koushik Barman, Xiang Wang, Rui Jia, Michael Mirkin Heterogeneous electrocatalysis and molecular redox catalysis have developed over the past several decades as two distinct ways to facilitate charge-transfer processes essential for energy conversion and storage. Whereas electrocatalytic reactions are driven by the applied voltage, molecular catalytic processes are driven by the difference between standard potentials of the catalyst and the reactant. Here, we demonstrate that the electrostatic potential drop across the double layer contributes to the driving force for electron transfer between a dissolved reactant and a molecular catalyst (e.g., ferrocene) immobilized directly on the electrode surface. Our density functional theory calculations show that varying the applied voltage alters the potential drop between the surface-bound molecular catalyst and the reactant and in some cases the chemical bonding between them, thereby increasing the reaction rate. These results suggest a promising new route for designing next-generation hybrid molecular/electrocatalysts. |
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