Neil W. Ashcroft
Department of Physics, Cornell
University
Abstract:
As is known from the organic domain, the
arrangements of the elements in combination are often exceedingly
complex even when the constituent elements themselves take up quite
simple structures. The same can be true in the inorganic domain;
intermetallics present especially interesting examples, and particularly
intermetallics of the lighter elements where quantum effects can be of
some importance.
Complexity, and the physical reasons driving it, can be probed via structural measurements particularly of the partial structure factors, though the standard assumptions made about the atomic scattering factors needed to extract these are not always secure. Especially interesting are cases where the ratio of valence (or itinerant) electrons to core (or bound) is quite high. When conditions are near classical, effective ion-ion interactions can be inferred from liquid phase partial pair-distribution functions via the 'classical inverse problem'. At variable density, induced by changes in external pressure, these interactions can be obtained as functions of state and insight then drawn about the nature of interactions in a complex phase below a melting curve, from information on the continuous symmetry state above.
The increasing flow of results from high pressure experimental studies present considerable challenges and opportunities to theory, many linked to the quite extraordinary density profiles taken up by valence electrons (impelled by pressure) to occupy somewhat unusual environments.
*Work supported by the Division of Materials Research, National Science Foundation.
abstract (pdf)
2008 Run
Nov 19th - Dec 22nd
