FIRST-PRINCIPLES STUDY ON ELECTRIC-FIELD-INDUCED STATES OF SILICON MICROCLUSTERS

1996 ◽  
Vol 03 (01) ◽  
pp. 389-393 ◽  
Author(s):  
KAZUYUKI WATANABE ◽  
TAKASHI ABE ◽  
TSUYOSHI OGINO ◽  
SAKURA TAKEDA
Keyword(s):  
Electric Field ◽  
Bond Length ◽  
Electric Fields ◽  
First Principles ◽  
Bending Mode ◽  
Bond Stretching ◽  
Bond Bending ◽  
Cohesive Energies ◽  
Present Simulation

The first-principles molecular dynamics (FPMD) method is applied to a Si dimer and a Si trimer in electrostatic fields to calculate the charge polarization, the stable structures, and the cohesive energies. It is found that the bond length of the dimer increases, and the bond length and the bond angle of the trimer decrease as the electric field increases. The obtained structural change due to electric fields is compatible with the change in the cohesive energy. The vibrational dynamics of the dimer and trimer are also studied. The bond-bending mode of the trimer is found to be more largely influenced by the electric field than the bond-stretching mode. The present simulation revealed a fundamental role of electric fields in manipulating microclusters.

scholarly journals Elucidating the Influence of Electric Fields toward CO2 Activation on YSZ (111)

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 271
Author(s):  
Nisa Ulumuddin ◽  
Fanglin Che ◽  
Jung-Il Yang ◽  
Su Ha ◽  
Jean-Sabin McEwen
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Heterogeneous Catalysts ◽  
Co2 Reduction ◽  
Total Density ◽  
Reverse Water Gas Shift ◽  
High Thermodynamic Stability ◽  
Shift Reaction ◽  
Water Gas

Despite its high thermodynamic stability, the presence of a negative electric field is known to facilitate the activation of CO2 through electrostatic effects. To utilize electric fields for a reverse water gas shift reaction, it is critical to elucidate the role of an electric field on a catalyst surface toward activating a CO2 molecule. We conduct a first-principles study to gain an atomic and electronic description of adsorbed CO2 on YSZ (111) surfaces when external electric fields of +1 V/Å, 0 V/Å, and −1 V/Å are applied. We find that the application of an external electric field generally destabilizes oxide bonds, where the direction of the field affects the location of the most favorable oxygen vacancy. The direction of the field also drastically impacts how CO2 adsorbs on the surface. CO2 is bound by physisorption when a +1 V/Å field is applied, a similar interaction as to how it is adsorbed in the absence of a field. This interaction changes to chemisorption when the surface is exposed to a −1 V/Å field value, resulting in the formation of a CO3− complex. The strong interaction is reflected through a direct charge transfer and an orbital splitting within the Olatticep-states. While CO2 remains physisorbed when a +1 V/Å field value is applied, our total density of states analysis indicates that a positive field pulls the charge away from the adsorbate, resulting in a shift of its bonding and antibonding peaks to higher energies, allowing a stronger interaction with YSZ (111). Ultimately, the effect of an electric field toward CO2 adsorption is not negligible, and there is potential in utilizing electric fields to favor the thermodynamics of CO2 reduction on heterogeneous catalysts.

scholarly journals Electric potential differences across auroral generator interfaces

2013 ◽  
Vol 31 (2) ◽  
pp. 251-261 ◽  
Author(s):  
J. De Keyser ◽  
M. Echim
Keyword(s):  
Electric Field ◽  
High Altitude ◽  
Electric Fields ◽  
Electric Potential ◽  
Equilibrium Configuration ◽  
Potential Difference ◽  
Field Profile ◽  
Electric Potential Difference ◽  
Electric Field Profile

Abstract. Strong localized high-altitude auroral electric fields, such as those observed by Cluster, are often associated with magnetospheric interfaces. The type of high-altitude electric field profile (monopolar, bipolar, or more complicated) depends on the properties of the plasmas on either side of the interface, as well as on the total electric potential difference across the structure. The present paper explores the role of this cross-field electric potential difference in the situation where the interface is a tangential discontinuity. A self-consistent Vlasov description is used to determine the equilibrium configuration for different values of the transverse potential difference. A major observation is that there exist limits to the potential difference, beyond which no equilibrium configuration of the interface can be sustained. It is further demonstrated how the plasma densities and temperatures affect the type of electric field profile in the transition, with monopolar electric fields appearing primarily when the temperature contrast is large. These findings strongly support the observed association of monopolar fields with the plasma sheet boundary. The role of shear flow tangent to the interface is also examined.

scholarly journals Can Electric Fields Drive Chemistry for an Aqueous Microdroplet?

2021 ◽  
Author(s):  
Hongxia Hao ◽  
Itai Leven ◽  
Teresa Head-Gordon
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Water Droplet ◽  
Reaction Rates ◽  
Surface Reactivity ◽  
Bulk Solution ◽  
Excess Charge ◽  
Electronic Effects ◽  
Rate Acceleration

Abstract Reaction rates of common organic reactions have been reported to increase by one to six orders of magnitude in aqueous microdroplets compared to bulk solution, but the reasons for the rate acceleration are poorly understood. We investigate the role of electric fields at water droplet surfaces that might explain the promotion of unusual reactive chemistry, along with changes in electric field profiles as a function of excess charge to model the electrospray fragmentation process. We find that electric field alignments along free O-H bonds at the surface yield field strength distributions that are ~30 MV/cm larger on average than that found for O-H bonds in the interior of the water droplet, consistent with greater surface reactivity. We emphasize the importance of both nuclear and electronic effects at the surface, and the non-linear coupling of intramolecular solute polarization with intermolecular solvent modes, as a necessary feature for predicting the higher field strengths at water droplet surfaces.

Study of the Non-Linearity on TiO2(0 0 1) Surface with Oxygen Defects: A First-Principles Study

NANO ◽  
2017 ◽  
Vol 12 (08) ◽  
pp. 1750097
Author(s):  
Yuehua Dai ◽  
Xu Zhang ◽  
Chengzhi Ma ◽  
Zhiyong Pan ◽  
Feifei Wang ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
First Principles ◽  
Electronic Structures ◽  
Oxygen Vacancies ◽  
Stark Effect ◽  
Energy Levels ◽  
Oxygen Interstitial ◽  
Oxygen Defects ◽  
Pseudopotential Calculations

First-principles plane-wave pseudopotential calculations were performed to study the energetics and electronic structures of oxygen defects on rutile TiO2(0 0 1). The influence of the material thickness on non-linearity (NL) was studied. With the increase in the thickness, the NL became stronger. Calculating the site-projected density of states by applying an external electric field showed that the NL of the bulk is due to the exchange of electrons between O 2p orbitals and Ti 3d orbitals. Finally, the influence of oxygen defects — oxygen vacancies (Vo), oxygen interstitials (Oi), and oxygen vacancies/oxygen interstitial (Vo[Formula: see text]Oi) pairs (Frenkel pair defects) — on the NL of TiO2 was studied. These results demonstrate that the band gap ([Formula: see text] of TiO2 became gradually narrower as the electric field increased. The Stark effect and defects can lead to the splitting of degenerate energy levels. Stronger electric fields increase the band splitting and reduce [Formula: see text]. With the increase in the Vo concentration, the decrease in the splitting amplitude and width of the energy level lead to weakening of the transfer of electrons between O and Ti atoms and optimizing the NL of TiO2. Therefore, the incorporation of Vo plays a significant role in improving the NL of TiO2.

scholarly journals Vacuum instability in a constant inhomogeneous electric field: a new example of exact nonperturbative calculations

2020 ◽  
Vol 80 (2) ◽  
Author(s):  
T. C. Adorno ◽  
S. P. Gavrilov ◽  
D. M. Gitman
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Transition Probabilities ◽  
Particle Creation ◽  
Field Configuration ◽  
Quantum Processes ◽  
Reflection And Transmission ◽  
Vacuum Instability ◽  
Klein Gordon

Abstract Basic quantum processes (such as particle creation, reflection, and transmission on the corresponding Klein steps) caused by inverse-square electric fields are calculated. These results represent a new example of exact nonperturbative calculations in the framework of QED. The inverse-square electric field is time-independent, inhomogeneous in the x -direction, and is inversely proportional to x squared. We find exact solutions of the Dirac and Klein–Gordon equations with such a field and construct corresponding in- and out-states. With the help of these states and using the techniques developed in the framework of QED with x-electric potential steps, we calculate characteristics of the vacuum instability, such as differential and total mean numbers of particles created from the vacuum and vacuum-to-vacuum transition probabilities. We study the vacuum instability for two particular backgrounds: for fields widely stretches over the x-axis (small-gradient configuration) and for the fields sharply concentrates near the origin $$x=0$$x=0 (sharp-gradient configuration). We compare exact results with ones calculated numerically. Finally, we consider the electric field configuration, composed by inverse-square fields and by an x-independent electric field between them to study the role of growing and decaying processes in the vacuum instability.

scholarly journals Role of inductive electric fields and currents in dynamical ionospheric situations

2007 ◽  
Vol 25 (2) ◽  
pp. 437-455 ◽  
Author(s):  
H. Vanhamäki ◽  
O. Amm ◽  
A. Viljanen
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Temporal Variations ◽  
Ionospheric Currents ◽  
Calculation Technique ◽  
Induced Field ◽  
Ionospheric Electric Field ◽  
Electric Fields And Currents ◽  
Current Systems

Abstract. We study the role of ionospheric induction in different commonly observed ionospheric situations. These include an intensifying electrojet, westward travelling surge (WTS) and Ω-band. We use data based, realistic models for these phenomena and calculate the inductive electric fields that are created due to the temporal variations of ionospheric currents. The ionospheric induction problem is solved using a new calculation technique that can handle non-uniform, time-dependent conductances and electric fields of any geometry. We find that in some situations inductive effects are not negligible and the ionospheric electric field is not a pure potential field, but has a significant induced rotational part. In the WTS and Ω-band models the induced electric field is concentrated in a small area, where the time derivatives are largest. In the electrojet model the induced field is significant over a large part of the jet area. In these examples the induced electric field has typical values of few mV/m, which amounts to several tens of percents of the potential electric field present at the same locations. The induced electric field is associated with ionospheric and field aligned currents (FAC), that modify the overall structure of the current systems. Especially the induced FAC are often comparable to the non-inductive FAC, and may thus modify the coupling between the ionosphere and magnetosphere in the most dynamical situations. We also present some examples with very simple ionospheric current systems, where the effect of different ionospheric parameters on the induction process is studied.

scholarly journals On the role of neutral flow in field-aligned currents

2018 ◽  
Vol 36 (1) ◽  
pp. 53-57 ◽  
Author(s):  
Anthony J. Mannucci ◽  
Olga P. Verkhoglyadova ◽  
Xing Meng ◽  
Ryan McGranaghan
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Rest Frame ◽  
Geomagnetic Storms ◽  
Electron Flow ◽  
Lower Ionosphere ◽  
Momentum Balance ◽  
Neutral Atmosphere ◽  
Magnetospheric Dynamics

Abstract. In this brief note we explore the role of the neutral atmosphere in magnetosphere–ionosphere coupling. We analyze momentum balance in the ion rest frame to form hypotheses regarding the role of neutral momentum in the lower ionosphere during geomagnetic storms. Neutral momentum that appears in the ion rest frame is likely the result of momentum imparted to ionospheric ions by solar wind flow and the resultant magnetospheric dynamics. The resulting ion-neutral collisions lead to the existence of an electric field. Horizontal electron flow balances the momentum supplied by this electric field. We suggest a possible role played by the neutral atmosphere in generating field-aligned currents due to local auroral heating. Our physical interpretation suggests that thermospheric neutral dynamics plays a complementary role to the high-latitude field-aligned currents and electric fields resulting from magnetospheric dynamics. Keywords. Ionosphere (ionosphere–magnetosphere interactions; polar ionosphere) – magnetospheric physics (magnetosphere–ionosphere interactions)

scholarly journals Ih interacts with somato-dendritic structure to determine frequency response to weak alternating electric field stimulation

2018 ◽  
Vol 119 (3) ◽  
pp. 1029-1036 ◽  
Author(s):  
Enrique H. S. Toloza ◽  
Ehsan Negahbani ◽  
Flavio Fröhlich
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Cellular Response ◽  
Current Injection ◽  
Field Stimulation ◽  
Electric Field Stimulation ◽  
Cation Current ◽  
Network Oscillations ◽  
Alternating Electric Field

Transcranial current stimulation (tCS) modulates brain dynamics using weak electric fields. Given the pathological changes in brain network oscillations in neurological and psychiatric illnesses, using alternating electric field waveforms that engage rhythmic activity has been proposed as a targeted, network-level treatment approach. Previous studies have investigated the effects of electric fields at the neuronal level. However, the biophysical basis of the cellular response to electric fields has remained limited. Here, we characterized the frequency-dependent response of different compartments in a layer V pyramidal neuron to exogenous electric fields to dissect the relative contributions of voltage-gated ion channels and neuronal morphology. Hyperpolarization-activated cation current (Ih) in the distal dendrites was the primary ionic mechanism shaping the model’s response to electric field stimulation and caused subthreshold resonance in the tuft at 20 ± 4 Hz. In contrast, subthreshold Ih-mediated resonance in response to local sinusoidal current injection was present in all model compartments at 11 ± 2 Hz. The frequencies of both resonance responses were modulated by Ih conductance density. We found that the difference in resonance frequency between the two stimulation types can be explained by the fact that exogenous electric fields simultaneously polarize the membrane potentials at the distal ends of the neuron (relative to field direction) in opposite directions. Our results highlight the role of Ih in shaping the cellular response to electric field stimulation and suggest that the common model of tCS as a weak somatic current injection fails to capture the cellular effects of electric field stimulation. NEW & NOTEWORTHY Modulation of cortical oscillation by brain stimulation serves as a tool to understand the causal role of network oscillations in behavior and is a potential treatment modality that engages impaired network oscillations in disorders of the central nervous system. To develop targeted stimulation paradigms, cellular-level effects must be understood. We demonstrate that hyperpolarization-activated cation current (Ih) and cell morphology cooperatively shape the response to applied alternating electric fields.

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