Warren E. Pickett
- Professor, Department of Physics
- University of California - Davis
- One Shields Avenue
- Davis CA 95616
- Tel: (530)752-0926
- Fax: (530)752-4717
| PhD || 1975 || SUNY Stony Brook
| MS || 1971 || Wichita State Univeristy
| BS || 1969 || Wichita State University
| || ||
Our Research Goals and Methods
The theory of the behavior of electrons in condensed matter is highly
developed, and the implementation in computer codes has progressed
enough, that a good deal of the important basic properties of materials
can be obtained from "first principles," that is, without input from
experiment. On the other hand, there are still many exceedingly
interesting phenomena that cannot yet be address from the first
Our aim is, first, to apply the successful computational theories
to further our understanding of condensed matter systems and to
obtain insight into what is still lacking, and then second, to
extend the method to describe properties more accurately and to
address more phenomena. This programme requires a broad outlook,
but once a project is chosen we focus on it in great detail.
Selected Visualizations of Work:
Isosurface plot of the charge rearrangement
due to covering a diamond surface with oxygen and then cesium.
The purple spheres represent carbon atoms (sorry about the hue). Oxygen
atoms are green; the cesium adsorbates are blue. All atoms were relaxed
to their minimum energy configuration. The isosurfaces show the charge
rearrangement when spherical Oxygen and cesium atoms are placed on the
diamond surface, then the charge is allowed to flow as it wants. The
'copper' colored surface indicates charge depletion, the 'silver'
colored one show charge accumulation. A complex charge dipole layer
results, which raises the potential of the interior with respect to
the vacuum. The resulting system is a negative electron affinity
system, in which any electron excited into the conduction bands
near the surface will spontaneously eject from the surface. This effect
is very useful for cold cathodes and for
flat panel displays, for
Step on the diamond (111) surface,
with colors indicating the local energy of the atom.
Work done with Brian Davidson.
Isosurface plot of the active electron
orbital in the electride Cs 3-crown-6. What is an electride?
It is an ionic crystal in which a molecule loses an electron and thereby
becomes the cation, and the electron locates itself in an
interstitial position and by itself, that is, without an atom or a
molecule, become the anion. It seems clear, from the joint
implication of our theoretical work and the experimental data, that
in this molecular crystal the valence electron of the Cs atom sits
in the open interstice and thereby stabilizes the crystal. The plot
shows an isosurface of the density of the 'electride state' in the
interstitial region of the crystal. Blue atoms are oxygen, red atoms
are carbon, orange atoms are hydrogen. Our results
also suggest that this system is a Mott insulator, and might form an
excellent realization of a system described by the simple
single band Hubbard
model without orbital degeneracy lurking to cause complications.
Work done with David Singh, Henry Krakauer, and Cree Haas.