A variety of physical phenomena involve multiple length and time scales
in their manifestation. Some examples, on which our recent work has
focused involve:
(a) the mechanical behavior of crystals and in particular the interplay
of chemistry and mechanical stress in determining the macroscopic brittle
or ductile response of solids, as in hydrogen-induced plasticity;
(b) the response of piezoelectric crystals tocompeting external electric
and mechanical pressure fields;
(c) the alteration of the structure and electronic properties of biological
macromolecules due to external forces, as in the conductivity of stretched
DNA nanowires.
In these complex physical systems, the changes in bonding and atomic
configurations at the microscopic level have profound effects on the
macroscopic properties, be they of mechanical or electrical nature.
Linking the processes at the two extremes of the length scale spectrum
is the only means of achieving a deeper understanding of these phenomena
and of ultimately being able to control them.
In this talk we will discuss the development of methodologies for simulations
across disparate length scales with the aim of obtaining a detailed description
of complex phenomena of the type mentioned above. The methodologies are based
on density functional theory approaches at the microscopic scale, on
molecular dynamics simulations at the mesoscopic scale, and on continuum
approaches at the macroscopic scale. We describe the key ideas behind the links
across the scales and how these are implemented in specific examples.
The systems and phenomena we will consider as representative examples are:
the role of defects and impurities in changing the ductility of metallic
solids like aluminum, the response of piezoelectrics like lead titanate to
competing electric and mechanical stress fields, and the role of external
stress in the conductivity of DNA nanowires.
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