On the construction of a bias potential for atomic system simulation by the hyperdynamics method

Hyperdynamics is the method of accelerated molecular dynamics simulation based on lowering energy barriers while performing the dynamic simulation of a nano/atomic system. A system with reduced energy barriers between different states is obtained by changing the potential of interaction, namely, by constructing the so-called bias potential. An approach allowing a bias potential to be obtained is considered. To demonstrate this method, the hyperdynamics simulation of the diffusion of an atom, adsorbed on a 2D crystal surface, and a vacancy, located in its bulk, is carried out. The results are compared with relevant results obtained by molecular dynamics. It is shown that the hyperdynamics approach makes it possible to obtain statistical results, similar to those provided by molecular dynamics. This allows the accelerated simulation of atomic systems to be conducted with minor losses in the accuracy of results.     

Rescattering for extended atomic systems

Laser-driven rescattering of electrons is the basis of many strong-field phenomena in atoms and molecules. Here, we will show how this mechanism operates in extended atomic systems, giving rise to effective energy absorption. Rescattering from extended systems can also lead to energy loss, which in its extreme form results in nonlinear light-induced trapping. Intense-laser interaction with atomic clusters is discussed as an example. We explain fast electron emission, seen in experimental and numerically obtained spectra, by rescattering of electrons at the highly charged cluster.     

Revised intermolecular potential with parameters depending on partial atomic charges for aromatic molecular systems

The practicablity and precision of the intermolecular potential was improved within the frame of an atom-atom approximation using 6-exp-1 type isotropic interatomic potentials without additional parameters. The improvement involves making the van der Waals parameters functions of the partial charges on constituent atoms supplement the classification of the parameter set, depending on atom type. The validity of the potential was confirmed with respect to crystal structures of polyacene (i.e., benzene, naphthalene, anthracene and tetracene) by molecular dynamics simulations.     

Magneto-electric response functions for simple atomic systems

We consider a simple atomic two-body bound state system that is overall charge neutral and placed in a static electric and magnetic field, and calculate the magneto-electric response function as a function of frequency. This is done from first principles using a two-particle Hamiltonian for both an harmonic oscillator and Coulomb binding potential. In the high frequency limit, the response function falls off as 1/ω ² whilst at low frequencies it tends to a constant value.     

First-principles molecular dynamics simulation of biased electrode/solution interface

First-principles molecular dynamics simulations have been carried out for water in contact with Pt(1 1 1) surface. To apply negative bias potential to the water/Pt interface, excess electrons were added to our slab model using the recently developed computational scheme called “effective screening medium (ESM)”. Water molecules located away from the surface reoriented themselves to screen the electric field, but they responded differently near the surface. Water molecules nearest to the surface, forming a distinct layered structure with the hydrogen atom directed to the surface, increased the density with increasing field. On these bases, we discuss microscopic aspects of the electric double layer.     

Interatomic potential for atomic collisions in real solids

An extremely simplified inter-atomic potential proposed recently has been modified so that it satisfied the basic properties like charge neutrality and unit screening function at origin (φ(0)= 1). The simplicity is retained to a great extent so that it can still be used for calculations on charged particle propagation in real solids with defects.     

Determination of the potential distribution of electron optical systems by agent-based simulation

We demonstrate that the potential distribution of electron optical systems can be quickly determined by agent-based simulation with relatively high accuracy. There is no need for the solution of large systems of algebraic equations. This method is especially useful for quick analysis of potential distributions and demonstration purposes.     

Towards a novel simulation approach for the transport of atomic states through polarized photons

A novel approach for transferring logic states from one quantum node to other is proposed. Logic states ‘0’ and ‘1’ are represented by two subspaces of the hyperfine states space of rubidium atom (⁸⁷Rb). The atom, placed at the center of a two-mode cavity, is excited by simultaneous application of two laser beams, one for each subspace. Based on the logic state of the atom, it makes a transition to a higher energy level within the corresponding subspace. When the atom relaxes back to a lower state within the subspace, a left- or right-circularly polarized photon is emitted depending on whether the initial state was logic ‘0’ or logic ‘1’. The polarized photon leaks out of the cavity, reaches the receive node and gets detected therein. Simulation results show the efficacy of the approach.     

Evolution of spin-dependent atomic wave packets in a harmonic potential

We have investigated theoretically the evolution of spin-dependent atomic wave packets in a harmonic magnetic trapping potential. For a Bose-condensed gas, which undergoes a Mott insulator transition and a spin-dependent transport, the atomic wavefunction can be described by an entangled single-atom state. Due to the confinement of the harmonic potential, the density distributions exhibit periodic decay and revival, which is different from the case of free expansion after switching off the combined harmonic and optical lattice potential.     

幅度调制原子力显微镜仿真平台

基于欧拉-伯努利模型,对幅度调制原子力显微镜( AM-AFM)进行建模,采用P]D控制器进行反馈控制,建立了一套幅度调制原子力显微镜仿真平台.仿真结果表明,该平台准确地模拟了AM-AFM探针接近样品和扫描样品的过程中探针的运动状态及AM-AFM的工作系统,可作为大学生做原子力显微镜实验的辅助工具,使学生对AM-AFM的...     

Calculations of magnetic moments for three-electron atomic systems.

The first fully correlated calculations of the magnetic moment in lithium are presented. Relative to the free-electron value, the Zeeman gJ factor for the ground state lithium gJ/g(e)-1 is calculated to a computational accuracy of 200 parts in 10(9), including relativistic and radiative corrections of orders alpha2, alpha2m/M, and alpha3. The isotope shifts in gJ are predicted precisely for various isotopes. The extensions to the first excited S state of lithium and the ground state of Be+ are made.     

Calculation method for the continuum states of atomic systems

In the present work, we develop a calculational method of solving the scattering equations for spherically symmetric potentials by expanding the solutions on Coulomb functions. We utilize a multistep integration scheme together with the standard partial wave analysis in a region where the potential term dominates. The method applies to any physical problem expressed as [? ² + V(r) + k ²]ψ(r) = 0, while the extension of the method to more general scattering problems is briefly discussed. At present, we demonstrate a two-step Coulomb-fitted integration scheme by calculating the short-range scattering phase shifts for various potentials V (r).     

Monte Carlo simulation of spin-aligned atomic hydrogen

The density dependent ground-state properties of spin-aligned atomic hydrogen are studied using the Monte Carlo technique for 32 and 128 atoms in a cube with periodic boundary conditions. The one-particle density matrix, the two-body correlation function, the structure and pairing function have been evaluated and are compared to other recent work. The total number of particles in the condensate is largest at a density 6·10^–3 Å^–3 and amounts to ⁰=2.03·10^–3Å^–3. In addition, the elementary excitation spectrum is discussed in the framework of the Brueckner-Sawada theory. The correct initial slope of the spectrum is obtained from variational results on the structure function. From these results one may tentatively conclude that the roton like part of the spectrum disappears at densities less than 10^–2 Å^–3.     

Instability of the uniform atomic chain with a convex interatomic potential

The cooperative character of the instability in a chain with a convex interatomic potrntial is shown. The low-temperature thermodynamics of such a chain is investigated. The interaction between such chains as a cause of the phase transition accompanied by doubling the lattice period in TlHF₂ is discussed.     

Continuous loading of a conservative potential trap from an atomic beam

We demonstrate the fast accumulation of 52Cr atoms in a conservative potential from a guided atomic beam. Without laser cooling on a cycling transition, a dissipative step involving optical pumping allows us to load atoms at a rate of 2×10(7) s(-1) in the trap. Within less than 100 ms we reach the collisionally dense regime, from which we produce a Bose-Einstein condensate with subsequent evaporative cooling. This constitutes a new approach to degeneracy where Bose-Einstein condensation can be reached without a closed cycling transition, provided that a slow beam of particles can be produced.     

Roughness simulation for thin films prepared by atomic layer deposition

The kinetic lattice Monte Carlo method for film growth simulation without taking crystallization into account was applied to study the roughness of the HfO₂ film grown by atomic layer deposition at 100–500°C from HfCl₄ and H₂O. The calculations were performed using a simplified kinetic mechanism of the growth of HfO₂ films obtained by reducing the detailed kinetic mechanism developed earlier. Ab initio quantum-chemical calculations were performed to determine the kinetic parameters of diffusion processes on the surface of hafnium oxide that could influence film roughness. Because of the special features of atomic layer deposition, the rate of film growth and film roughness were finite even if surface relaxation was ignored. It was found that, irrespective of the temperature, the diffusion of hydrogen and adsorbed HfCl₄ complexes did not change the profile of the growing film and only insignificantly increased the mean rate of growth. The results obtained were also qualitatively applicable to zirconium dioxide at fairly low (≤100°C) temperatures in the absence of crystallization.     

Classical simulation of atomic beam focusing and deposition for atom lithography

We start from the intensity distribution of a standing wave (SW) laser field and deduce the classical equation of atomic motion. The image distortion is analyzed using transfer function approach. Atomic flux density distribution as a function of propagation distance is calculated based on Monte-Carlo scheme and trajectory tracing method. Simulation results have shown that source imperfection, especially beam spread, plays an important role in broadening the feature width, and the focus depth of atom lens for real atomic source is longer than that for perfect source. The ideal focal plane can be easily determined by the variation of atomic density at the minimal potential of the laser field as a function of traveling distance.     

Nondestructive and complete Bell-state analysis for atomic qubit systems

This paper realizes a nondestructive and complete Bell-state analysis for atomic qubit systems by a designed nondestructive and complete Bell-state analyser. In the scheme, Bell states are completely discriminated by two bits of classical informations which comes from the locality single atom detection on two auxiliary atoms, during which the Bell states are not affected. The needed devices are well within the bounds of current technology, and then the scheme is experimentally feasible.     

On the chemical potential of atomic ions

The following relation between the chemical potential μ(Z, N) of an atomic ion with nuclear charge Z and N electrons and their partial derivatives (?μ/?N)_Z and (?μ/?Z)_N has been derived by March within the context of the Thomas-Fermi approximation $\text{Z(?μ/?Z)}{}_{\mathrm{N}}\text{+N(?μ/?N)}{}_{\mathrm{Z}}\text{=}\text{3}\text{4}\text{μ}$. We have performed a numerical test which shows that the same relation is also approximately fulfilled in other density functional models more sophisticated than the Thomas-Fermi model.     

Semi-exponential basis for highly accurate computations of three-electron atomic systems

An advanced basis set of semi-exponential radial functions is proposed and applied to highly accurate computations of three-electron atomic systems. This set is found to be significantly more effective in highly accurate, bound state computations of three-electron atomic systems, than currently used set of Hylleraas radial functions.