A method for studying electron-density-based dynamics of many-electron systems in scaled cylindrical coordinates

The combination of quantum fluid dynamics and density functional theory had led to the formulation of a single time-dependent equation, the generalized nonlinear Schrödinger equation (GNLSE). In this paper, the above GNLSE is written as a nonlinear diffusion-type equation in appropriately scaled cylindrical coordinates and evolved in imaginary time to obtain the electronic energies, densities and other properties of all the noble gas atoms. The close agreement of the values obtained with those from the literature implies that the same method can be used in real time to study the density-based dynamics of many-electron systems in axially symmetric external fields such as intense laser fields, with relatively less computational effort

A numerical study of time-dependent schrödinger equation for multiphoton vibrational interaction of no molecule, modelled as morse oscillator, with intense far-infrared femtosecond lasers

For the NO molecule, modelled as a Morse oscillator, time-dependent (TD) nuclear Schrödinger equation has been numerically solved for the multiphoton vibrational dynamics of the molecule under a far-infrared laser of wavelength 10503 nm, and four different intensities, I = 1 × 108, 1 × 1013, 5 × 1016, and 5 × 1018 W cm-2 respectively. Starting from the vibrational ground state at zero time, various TD quantities such as the norm, dissociation probability, potential energy curve and dipole moment are examined. Rich high-harmonics generation (HHG) spectra and above-threshold dissociation (ATD) spectra, due to the multiphoton interaction of vibrational motions with the laser field, and consequent elevation to the vibrational continuum, have been obtained and analysed

Does the classically chaotic Henon-Heiles oscillator exhibit quantum chaos under intense laser fields?

The quantum dynamics of an electron moving under the Henon-Heiles (HH) potential in the presence of external time-dependent (TD) laser fields of varying intensities have been studied by evolving in real time the unperturbed ground-state wave function f (x, y, t) of the HH oscillator. The TD Schrodinger equation is solved numerically and the system is allowed to generate its own wave packet. Two kinds of sensitivities, namely, sensitivity to the initial quantum state and to the Hamiltonian, are examined. The threshold intensity of the laser field for an electron moving in the HH potential to reach its continuum is identified and in this region quantum chaos has been diagnosed through a combination of various dynamical signatures such as the autocorrelation function, quantum 'phase-space' volume, 'phase-space' trajectory, distance function and overlap integral (akin to quantum fidelity or Loschmidt echo), in terms of the sensitivity towards an initial state characterized by a mixture of quantum states (wave packet) brought about by small changes in the Hamiltonian, rather than a 'pure' quantum state (a single eigenstate). The similarity between the HH potential and atoms/molecules in intense laser fields is also analyzed

Short-term PsychoEducation for Carers To Reduce Over Medication of people with intellectual disabilities (SPECTROM): study protocol

Introduction Psychotropic medications that are primarily licenced for the treatment of psychiatric disorders are used widely (32%–85%) among people with intellectual disabilities (ID) often for the management of problem (challenging) behaviour in the absence of a psychiatric disorder. Care staff play a pivotal role in the prescribing process. Currently, no staff training programme exists to address the issue of overprescribing of psychotropic medication in people with ID, thus highlighting an urgent need for developing a psychoeducational programme (PEP) specifically designed to address this issue. We propose to develop a PEP for care staff using the methodology described in the UK Medical Research Council guide for complex interventions. Methods and analysis The development of the PEP will involve (1) gathering information on available relevant training programmes, (2) running four focus groups with care staff and other professionals to establish the content and format of the PEP, and (3) organising a co-design event involving all relevant stakeholders to discuss the format of the PEP. A core project team will develop the PEP under guidance from the PEP Development Group which will consist of 10–12 relevant stakeholder representatives. Feedback from selected stakeholders on a draft PEP will allow us to refine the PEP before implementation. The PEP will have web-based modules supplemented by face to face training sessions. When the final draft is ready, we will field test the PEP on six to eight care staff from community care homes for people with ID. After completing the field test, we will run a focus group involving participants in the PEP to get feedback on the PEP. Ethics and dissemination Ethics approval for this study was waived by the UK Health Regulatory Authority as the study does not collect any patient related information and only include care staff outside the UK NHS. This will be the first ever such universally freely available PEP supported by training manual and slides

Translational Entanglement of Dipole-Dipole Interacting Atoms in Optical Lattices

We propose and investigate a realization of the position- and momentum-correlated Einstein-Podolsky-Rosen (EPR) states [Phys. Rev. 47, 777 (1935)] that have hitherto eluded detection. The realization involves atom pairs that are confined to adjacent sites of two mutually shifted optical lattices and are entangled via laser-induced dipole-dipole interactions. The EPR "paradox" with translational variables is then modified by lattice-diffraction effects, and can be verified to a high degree of accuracy in this scheme.Comment: 4 pages, 3 figures, to be published in PR

Stripped ion-helium atom collision dynamics within a time-dependent quantum fluid density functional theory

A nonperturbative, time-dependent (TD) quantum mechanical approach is described for studying the collision dynamics between the He atom and a fully stripped ion. The method combines quantum fluid dynamics and density functional theory to solve two coupled equations: one for the trajectory of the projectile nucleus and the other for the electronic charge distribution of the target atom. The computed TD and frequency-dependent properties provide detailed features of the collision process. Inelastic and ionization cross sections are also reported

Femtosecond quantum fluid dynamics of helium atom under an intense laser field

A comprehensive, nonperturbative, time-dependent quantum mechanical (TDQM) approach is proposed for studying the dynamics of a helium atom under an intense, ultrashort (femtoseconds) laser pulse. The method combines quantum fluid dynamics (QFD) and density functional theory. It solves a single generalized nonlinear Schrödinger equation of motion (EOM), involving time and three space variables, which is obtained from two QFD equations, namely, a continuity equation and an Euler-type equation. A highly accurate finite difference scheme along with a stability analysis is presented for numerically solving the EOM. Starting from the ground-state Hartree-Fock density for He at t=0, the EOM yields the time-dependent (TD) electron density, effective potential surface, difference density, difference effective potential, ground-state probability, (r), magnetic susceptibility, polarizability, flux, etc. By a Fourier transformation of the TD dipole moment along the linearly polarized-field direction, the power and rate spectra for photoemission are calculated. Eleven mechanistic routes for photoemission are identified, which include high harmonic generation as well as many other spectral transitions involving ionized, singly excited, doubly excited (autoionizing), and continuum He states, based on the evolution of the system up to a particular time. Intimate connections between photoionization and photoemission are clearly observed through computer visualizations. Apart from being consistent with current experimental and theoretical results, the present results offer certain predictions on spectral transitions which are open to experimental verification

Quantum fluid dynamics within a relativistic density-functional framework

The authors explore certain interconnections between density-functional theory and quantum fluid dynamics of many-electron systems, in the relativistic domain following the hydrodynamical approach adopted by Takabayashi for the one-particle Dirac equation. In order to build a 'classical' hydrodynamical interpretation, the spinor formulation is transformed into a tensor formulation by defining a number of density functions (local observables). These lead to six 'classical' fluid dynamic equations, together with two subsidiary conditions, for a complete specification of the system. The various density functions and the hydrodynamical equations are physically interpreted. The relativistic hydrodynamics discussed here correspond to a 'spinning' fluid. The net many-electron fluid consists of components each of which is characterised by fluid dynamic quantities corresponding to each spinor. The net hydrodynamical quantities are obtained by summing over the occupied spinors. Thus, the earlier nonrelativistic 'classical' picture of the many-electron fluid as a collection of individual fluid components is also valid in the relativistic domain

Electron transport in sub-micron GaAs channels at 300 K

Transient velocity-field characteristics have been computed for GaAs channels having lengths of 0.1, 0.2, 0.5, 1, and 20 µm for electric fields between 1 and 50 kV/cm at 300 K. The results are compared with earlier calculations and the significant features of the computed results are discussed. It is found that the electron motion for all channel lengths and for all fields is significantly affected by collisions. The threshold field for negative differential mobility increases, and the magnitude of the differential mobility decreases with decrease in the length of the sample. The maximum steady-state velocity increases with decrease in the length and may be as high as 5.4×107 cm/s for 0.1 µm samples

Position dependence of average electron velocity in a submicrometer GaAs channel

The Monte Carlo method has been applied to obtain the average electron velocity at different positions of a submicrometer GaAs channel in the presence of a position independent electric field. Velocity-distance curves are presented for channel lengths of 0.1, 0.2, and 0.5 µm and for lattice temperatures of 300 and 77 K. The curves show significant effects of collisions and boundary conditions