| Basic Energy
Sciences
NERSC provides computational support
for a large number of materials sciences and chemical sciences
projects sponsored by DOE’s Office of Basic Energy Sciences.
Highlights this year include the first complete explanation
of the unusual superconducting properties of magnesium diboride;
the first comparison with experimental measurements of a fully
detailed simulation of fluid viscosity; the first determination
of the magnetic structure of a superconductor from first-principles
calculations; the first ab initio
molecular dynamics simulation of low-energy deposition of metal
clusters on a solid surface; and an important contribution to
the study of the relationship between microstructure and magnetism
in nanosystems.
The Origin of the Anomalous Superconducting
Properties of MgB2
The quest for high-temperature superconductors is one of
the grand challenges of materials science. Magnesium diboride
(MgB2) differs from ordinary metallic superconductors
in several important ways, including its high transition temperature,
Tc = 39 oK, and its multiple
superconducting energy gaps. Understanding why MgB2
behaves as it does opens the possibility of creating new superconducting
materials with analogous electronic structure.
Choi et al. are the first researchers to successfully explain
the superconducting transition temperature and energy gaps
(Figure 1) of MgB2, along with its isotope effects, quasiparticle
density of states, specific heat, and temperature dependencies.
Using first principles pseudopotential density-functional
method coupled with a fully anisotropic Eliashberg formalism,
they found that the momentum-dependent electron-phonon interactions
and the anharmonicity of phonons in MgB2 are the most important
material properties that determine the superconducting properties.
Their calculated superconducting properties are all in agreement
with corresponding experiments. Their analysis suggests that
layered materials based on boron, carbon, and nitrogen may
exhibit comparable or higher transition temperatures.
INVESTIGATORS
M. L. Cohen, S. G. Louie, and D. Roundy, University of California,
Berkeley, and Lawrence Berkeley National Laboratory; H. J.
Choi and H. Sun, University of California, Berkeley.
PUBLICATION
H. J. Choi, D. Roundy, H. Sun, M. L. Cohen, and S. G. Louie,
“The origin of the anomalous superconducting properties
of MgB2,” Nature 418, 758 (2002).
URL
http://civet.berkeley.edu
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