Car-Parrinello Molecular Dynamics in a Finite Homogeneous Electric Field

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

Long-range electrostatic interactions critically affect polar materials. However, state-of-the-art atomistic potentials, such as neural networks or Gaussian approximation potentials employed in large-scale simulations, often neglect the role of these long-range electrostatic interactions. This study introduces a framework derived from first principles to evaluate the contribution of long-range electrostatic interactions to total energies, forces, and stresses. The model is designed to integrate seamlessly w

Suprathermal ions, i.e. ions with energies exceeding those of the bulk plasma, arise in diverse natural and laboratory plasmas ranging from the solar wind to magnetic confinement fusion (MCF) devices. In tokamaks, they are generated by external heating systems and fusion reactions, and a thorough characterization of their dynamics is crucial for safe operation. In tokamaks, the core plasma is separated from the walls by the last closed flux surface (LCFS), which exhibits a null point (X-point) in the poloid

Electrons and phonons constitute the most fundamental degrees of freedom in the material world, underpinning the technological applications that have shaped everyday life. This thesis explores the emerging electron and phonon physics in novel materials, demonstrating the failure of many conventional treatments and common approximations. The first part develops the theoretical toolbox for modelling microscopic electron and phonon interactions as well as their transport. Specifically, we introduce a robust an

The production of reactive species in nanosecond, repetitively pulsed plasmas is of decisive importance in tailoring such discharges to different applications. In this paper, we examine the features and advantages of using a nanosecond discharge at moderate pressure as a tool for measuring the G-value. The N-atom production in a pure N2, nanosecond pulsed plasma at a moderate pressure of 20 mbar and high reduced electric field of 180 +/- 20 Td is adopted as the test case. The atomic nitrogen density is meas

We report the multiferroic properties of 12R-type hexagonal Ba(Ti1/3Mn2/3)O3-delta found in Mn-doped BaTiO3 series samples. Hysteresis measurements reveal the coexistence of weak ferromagnetism and ferroelectricity at room temperature. Furthermore, frequen ...

We present a versatile high voltage sample stick that fits into all cryomagnets and standard cryostats at the Swiss Spallation Neutron Source, Paul Scherrer Institut, and which provides a low effort route to neutron scattering experiments that combine electric field with low temperature and magnetic field. The stick allows for voltages up to 5 kV and can be easily adapted for different scattering geometries. We discuss the design consideration and thermal behavior of the stick, and give one example to showc

RF microelectromechanical systems (MEMS) capacitive switches for two different dielectrics, aluminum nitride (AlN) and silicon nitride (Si3N4), are presented. The switches have been characterized and compared in terms of DC and RF performance (5-40 GHz). Switches based on AlN have higher down-state capacitance for similar dielectric thicknesses and provide better isolation and smaller insertion losses compared to Si3N4 switches. Experiments were carried out on RF MEMS switches with stiffening bars to preven

We calculate from first principles the nonlinear piezoelectric response of ferroelectric PbTiO3 for the case of a polarization-enhancing electric field applied along the tetragonal axis. We focus mainly on the case of fixed in-plane lattice constants, corr ...

From small-angle neutron scattering studies of the flux line lattice (FLL) in CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain the field and temperature dependence of the FLL form factor (FF), which is a measure of the spatial ...

The occurrence of an ultrathin SiO2 oxide layer at the interface between silicon and high-k dielectrics in metal-oxide-semiconductor devices contributes to degrading the capacitance of the gate stack. In this work, we investigate the dielectric and infrared properties of atomically thin SiO2 layers on Si(100) through a fully quantum-mechanical description. For this purpose, we construct atomistic models of the Si(100)-SiO2 interface on the basis of available experimental data, by using both classical and fi

We study the effect of a magnetic field (applied along the c axis) on the low-energy, incommensurate magnetic fluctuations in superconducting La1.82Sr0.18CuO4. The incommensurate peaks at 9 meV, which in zero field were previously shown to sharpen in q on cooling below T-c [T. E. Mason , Phys. Rev. Lett. 77, 1604 (1996)], are found to broaden in q when a field of 10 T is applied. The applied field also causes scattered intensity to shift into the spin gap. We point out that the response at 9 meV, though occ

During the last decade the field of computational chem. has experienced an enormous progress. Due to the exponential increase in computer power and the development of new computational methods it has now become possible to treat many complex chem. and biol. problems on an accurate and realistic level. Ab initio mol. dynamics simulations based on d. functional theory are among the most powerful of these new tools. Using parallel computers, systems of a few hundred of atoms can be studied routinely. By extend

In certain power applications, Bi-2223 conductors carrying AC current will be subjected to external magnetic fields, whose orientation and conductor’s geometry are of major significance for the AC loss magnitude. This paper investigates the influence of the geometry and aspect ratio of non-twisted Bi-2223 conductors in reducing the AC loss for such applications. A numerical model of high-Tc materials has been used in FEM simulations. The model incorporates power-law E-J characteristics with Jc defined by bo

We develop a fully vectorial formalism for the investigation of electromagnetic scattering in polarizable backgrounds, i.e., where the scatterers are not in vacuum but situated in a medium with a dielectric permittivity different from unity. Our approach is based on the Green's tensor technique and the corresponding Green's tensors for two-dimensional (2D) and three-dimensional (3D) systems are developed. The analysis of 2D systems is not restricted to the case where transverse electric (TE) and transverse

During the past five years, we have developed in our laboratory a new type of solar cell that is based on a photoelectrochemical process. The light absorption is performed by a monolayer of dye (i.e., a Ruthenium complex) that is adsorbed chemically at the surface of a semiconductor (i.e., titanium oxide (TiO2)). When excited by a photon, the dye has the ability to transfer an electron to the semiconductor. The electric field that is inside the material allows extraction of the electron, and the positive ch

A comprehensive micro-macroscopic model of the continuous hardening of 3d-axisymmetric steel components by induction heating has been developed. At the macroscopic scale, the Maxwell and heat flow equations are solved using a mixed numerical formulation : the inductor and the workpiece are enmeshed with finite elements (FE) but boundary elements (BE) are used for the solution of the electromagnetic equations in the ambient air. This method allows the inductor to be moved with respect to the workpiece withou

We investigated the I-V characteristics of the double barrier stair-well structure. Resonant tunneling current is achieved by application of an electric field, which increases the transmission under positive bias and decreases it under the reverse bias. This asymmetry can be used for rectification and the device works as a quantum diode. Furthermore, the same structure can perform, under negative bias, resonant tunneling processes with different characteristics.

Different formulations of the field-to-transmission-line coupling equations are reviewed and discussed. An equivalent formulation is derived in which the source terms (or forcing functions) are expressed in terms of the magnetic excitation field. This formulation is particularly useful for evaluating field-to-transmission-line coupling when the exciting field is determined experimentally, since only the measurement of the electric field-generally easier to measure than the electric field-is necessary

We consider the density of states of Schr6dmger operators with a uniform magnetic field and a random potential with a Gaussian distribution. We show that the restriction to the states of the first Landau level is eqmvalent to a scaling hmit where one looks at the density of states near to the energy of the frst Landau level and simultaneously lets the strength of the coupling to the random potential go to zero. We also consider a different limit where we look at the suitably normalised density of states nea

We give explicity the polarization dependence of two-photon subband-subband transitions in semiconductor quantum wells. We consider transitions from heavy-hole subbands as well as from light-hole subbands. We study the polarization dependence in the case of absorption of one photon having an energy of the order of the band gap and one having an energy of the order of the subband separation. We show that the absorption structure depends on the polarization of the low-energy photon. We also give, in the case

Car-Parrinello Molecular Dynamics in a Finite Homogeneous Electric Field

Chat with Graph Search

Electrostatic interactions in atomistic and machine-learned potentials for polar materials

Fast ion transport in complex magnetic field configurations in TORPEX

Thermodynamics and Exotic Transport Phenomena in Emerging Materials

Nanosecond Discharges as a Tool for Measuring Energy Efficiency (g-values) at High Reduced Electric Fields Based on Nitrogen Dissociation

Polaron response dominated multiferroic property in 12R-type hexagonal Ba(Ti1/3Mn2/3)O3-delta ceramics

Note: Versatile sample stick for neutron scattering experiments in high electric fields

RF MEMS Shunt Capacitive Switches Using AlN Compared to Si3N4 Dielectric

First-principles study of high-field piezoelectricity in tetragonal PbTiO3

Observations of Pauli paramagnetic effects on the flux line lattice in CeCoIn5

Dielectric and infrared properties of ultrathin SiO2 layers on Si(100)

Evidence for an incommensurate magnetic resonance in La2-xSrxCuO4

Mixed quantum mechanical/molecular mechanical simulation of biological systems

Geometry considerations for transport current applications of Bi-2223 conductors with anisotropic Jc(B) in external magnetic field

Electromagnetic scattering in polarizable backgrounds

Nanocrystalline titanium oxide electrodes for photovoltaic applications

Modelling of electromagnetic heating, cooling and phase transformations during surface hardening of steels

The I-V Characteristics of Double-Barrier Stair-Wells

Formulation of the field-to-transmission line coupling equations in terms of magnetic excitation field

Density of states of random Schroedinger operators with a uniform magnetic field

Polarization Dependence of 2-Photon Transitions in Quantum-Wells