Several ab initio methods exist for calculating energies of
atoms, molecules, and solids. We are testing a new technique
that uses Feynman path integrals. This new many-body method
includes finite temperature and can be much more accurate
than other popular techniques. We calculated the ground
state energies of the first four atoms in the periodic
table, H, He, Li and Be with Path Integral Monte Carlo
simulations. We find total energies that are more accurate
than both density functional theory and Hartree-Fock. We are
also studying diatomic molecules to see thermal effects on
geometry and polarization.
[S5.002] Monte Carlo Simulation of Wave Damping in a Dilute Gas
Ryan Clary (Utah Valley State College), Ross Spencer (Brigham Young University)
A computer simulation has been written that simulates the
evolution of a perturbed dilute gas using the
Direct-Simulation Monte Carlo method, with the ultimate goal
of adding collisions to a simulation of ultra-cold plasmas.
As a test, it has been used to study fluid dynamic affects
in one dimension using a small velocity perturbation so that
comparison with standard gas-dynamic theory is possible.
This comparison has been used to investigate the limitations
on certain simulation parameters such as cell size, size of
each time step, number of simulation particles, and
mean-free-path. The simulation and the theory agree well
when the mean-free path is a small fraction of the sound
wavelength, but for long mean free paths the simulation and
the theory diverge. As an illustration, the famous ``bell in
a bell jar'' demonstration will be examined to see if wave
damping might play a role.
[S5.003] Low-field orientation dependence of ^3He relaxation in spin-exchange cells
J. Teter, R. E. Jacob, B. Saam (University of Utah), W. C. Chen, T. R. Gentile (NIST)
^3He, a spin-\frac12 noble gas, can be highly
polarized by spin-exchange optical pumping (SEOP) for use in
applications such as magnetic resonance imaging (MRI). The
ability to maximize and maintain the ^3He polarization is
crucial when using ^3He as a signal source for MRI. We
have observed a significant dependence of ^3He
longitudinal relaxation times (T_1) in glass SEOP cells
due only to the physical orientation of the cell in a
\approx30 G measurement magnetic field. In contrast with
previous work, the cells either had no previous exposure to
higher fields or were thoroughly degaussed prior to T_1
measurements. The presence of Rb metal and heating of the
cells associated with the SEOP process is necessary to
produce this low-field orientation dependence. Our data
suggest that the hysteretic (R. E. Jacob, \emphet al.,
Phys. Rev. Lett. \underline87 143004 (2001)) magnetic
relaxation sites involved here may be the dominant cause of
wall-relaxation in SEOP cells at any field.
[S5.004] Quantum Monte Carlo treatment of Spin Orbit Interaction
Raghu Chatanathody, John Shumway, Kevin Schmidt (Department of Physics and Astronomy, Arizona State University)
We treat the spin-orbit interaction in many-electron systems
within variational and diffusion Monte Carlo. We explicitly
include the spin degrees of freedom by putting a
two-component spinor on each electron. In our all-electron
atomic calculations, the spin-orbit interaction is a
parameter-free relativistic correction to the Schrodinger
equation. This interaction is simply the local electric
field at each electron, which appears as a magnetic field in
that electron's rest frame. Thus our many-body calculations
give the atomic spin-orbit coupling strengths by evaluating
the electric field from the nucleus and all other electrons,
and coupling to the electron's spin and velocity. We
illustrate this method on first and second row atoms, and
discuss its potential applications to solids and molecules.
(Work supported by DARPA/ONR )
[S5.005] Laser Beam Energy Deposition by Ray Tracing in a Laser-Produced Plasma
Zafar Yasin (Department of Physics, UNLV , Las Vegas.)
Uniformity of energy deposition in the coronal plasma
surrounding the pellet surface is crucial for meeting Lawson
criteria for ICF. Energy deposition can be computed by
tracing laser rays through the plasma using approximation of
geometrical optics. Ray tracing equations for a focused
laser beam propagating through the plasma are derived, for
various beam target configurations. S-polarized laser light
is considered for energy absorption by inverse
bremstrahlung, and p-polarized for resonance absorption. A
ray tracing code has been used to see optical interference
effects on the uniformity of energy deposition.
[S5.006] Semi-classical Study of Electron Blurring in the Magnetic Field of a Current Ring
Daniel James, Jean-Francois Van Huele (Brigham Young University)
We develop a semi-classical method for determining small quantum variations around classical trajectories and apply it to the dynamical variables of an axial beam of charged particles passing through the center of a current ring. We obtain a complete set of coupled differential equations that describe the evolution of the beam and we solve numerically to determine the blurring introduced by the small quantum corrections. We compare the longitudinal blurring of the beam to the spin separation under the influence of the inhomogenous magnetic field. The results will be illustrated with animations. Implications on the feasability of a longitudinal Stern-Gerlach experiment with electrons will be discussed.