*Before*

As pointed out by James Langer in a recent editorial of Physics Today,
scientific computing is now on a par with laboratory experiment and
mathematical theory as a tool for research in science and engineering:
"The computer is literally providing a new window through which we can
observe the natural world in exquisite detail." [1].
Simulations can substitute for experiments that are impossible or
impracticable. They can help interpret experiments, thus providing
*virtual laboratories* that complement real laboratories
and mathematical theories.
Examples will illustrate quantum simulations, that is, simulations at
the *microscopic level*, driven by the laws of quantum mechanics.
In particular, I will describe recent work on
fluids and solids under pressure (predicting structural properties);
microfractures in disordered solids;
dynamics and stability of nanoparticles;
conformation and dynamics of the DNA backbone.
These simulations, together with many others appeared in the literature
of the last two decades, highlight the important role of *
computational quantum mechanics* [2] in addressing problems in
condensed matter physics, materials science and chemical physics.

[1] "Computing in Physics: are we taking it too seriously? Or not

seriously enough," J. Langer, Physics Today, July 1999.

[2] "Computational material science: the era of applied quantum

mechanics," J. Bernholc, Physics Today, September 1999.

*After*

Scientific computing is now on a par with laboratory experiment and
mathematical theory as a tool for research in science and engineering.
Simulations can substitute for experiments that are impossible or
impracticable. They can help interpret experiments, thus providing
*virtual laboratories* that complement real laboratories
and mathematical theories.

Examples illustrate quantum simulations, that is, simulations at
the *microscopic level*, driven by the laws of quantum mechanics:
(1) fluids and solids
under pressure, (2) microfractures in disordered solids, (3) dynamics
and stability of nanoparticles, and (4) conformation and dynamics of
the DNA backbone. These simulations, together with those in the last
two decades, highlight the important role of *computational quantum
mechanics* in addressing problems in condensed matter physics,
materials science and chemical physics.

*Before *

CeRhIn_{5}, CeIrIn_{5}, Ce_{2}RhIn_{8}, and
Ce_{2}IrIn_{8} are members of a new family of heavy
Fermion materials that are tetragonal derivatives of CeIn_{3}.
At ambient pressure CeRhIn_{5} orders antiferromagnetically at
T_{N}=3.8 K out of a state with a Sommerfeld coefficient of
order 200 mJ/mol-K^{2}. With applied pressure, the electrical
resistivity develops a peak near 30 K that initially moves to lower
temperature with increasing pressure, unlike other Ce-based materials.
T_{N} is nearly pressure independent to 15 kbar, at which point a
first-order like transition to a superconducting state with
T_{c}=2.1 K is observed. CeIrIn_{5} has a Sommerfeld
coefficient of order 700 mJ/mol-K_{2} and displays bulk
superconductivity below 400 mK. The superconducting transition
sharpens and moves to higher temperature with applied pressure.
Finally, Ce_{2}RhIn_{8} orders antiferromagnetically
at 2.8 K, while Ce_{2}IrIn_{8} remains paramagnetic to
100 mK. The variety of these ground states and their evolution with
pressure emphasizes the role of spatial dimensionality in determining
the ground state of heavy Fermion materials.

*Before *

Heavy Fermion materials have "heavy" electrons -- the specific heat coefficient at low temperature is dramatically enhanced from a typical metallic value by factors of 100-1000 -- due to the interaction of conduction electrons with localized magnetic moments. Magnetic and non-magnetic order compete in these materials. When magnetic order is suppressed, unconventional superconductivity can emerge. This competition plays out dramatically in a recently discovered family of compounds that are layered, in strong similarity to the high-temperature superconduting cuprates. In both, reduced dimensionality is an important component in understanding their properties.

*Before *

An account is given of the use of neutron diffraction techniques in the study of the structure of inorganic amorphous solids, involving both steady-state and pulsed neutron sources. The quantification of amorphous solids structures is discussed and the various types of structural model employed in the interpretation of neutron diffraction data are outlined, using examples taken from a wide range of materials including amorphous semiconductors, oxide, halide, chalcogenide and metallic glasses. Special emphasis is placed on the correct procedures for the intercomparison of models and experiments and it is shown that the greatest barrier to progress in understanding the structure of amorphous solids lies not with the diffraction data themselves but in the development of new modeling techniques in which parameters can be varied in a systematic way.

*After*

Data on the the structure of inorganic amorphous solids comes from both steady-state and pulsed neutron diffraction. The use of models to characterize structure is illustrated for materials as diverse as amorphous semiconductor, chalcogenide glasses or metallic glasses. The greatest challenge to understanding the structure of amorphous solids lies not in the better diffraction techniques but in new modeling techniques that allow the parameters to be varied in a systematic way.

Improving the Abstract

<http://www.physics.ohio-state.edu/~wilkins/writing/Handouts/abstracts.html>

[Tuesday, 18-Sep-2018 15:11:30 EDT]

Edited by: wilkins@mps.ohio-state.edu on Sunday, 01-May-2011 16:04:39 EDT