Today, density functional theory (DFT) based calculations allow us to study
a number of metal alloy properties, as e.g.\ formation enthalpies,
or electronic and elastic properties of intermetallic compounds.
However, such so-called ab-initio calculations can only be applied as long as
the alloy structure requires only small unit cells for the
crystallographic description. It will be demonstrated how
this limitation can be overcome without giving
up the accuracy of DFT calculations by combining them with
so-called Cluster Expansion (CE) methods and Monte-Carlo simulations.
This concept gives access to both,
huge parameter-spaces (e.g. for ground-state searches)
and systems containing more than a million of atoms
(e.g. for microstructure studies). It permits to treat
alloy properties which possess a delicate
temperature-dependence like mixing enthalpies, short-range order,
coherent phase boundaries, or microstructure evolution
{\em without} any empirical parameters as input, but
with an accuracy that allows the {\em quantitative} prediction of
experimental results. The presented examples reach from fcc- and bcc-based
disordered alloys up to intermetallic compounds.
Regarding microstructures the focus is
on so-called coherent precipitates whose size-shape
relations can be of technical relevance in alloys like Al-Li
or Al-Zn. At the moment, the presented methods are extended to alloy surfaces
for investigations of ordering phenomena at surfaces and surface
segregation, i.e. the deviation of the alloy's composition
in the near-surface region compared to the bulk. The first example
represents the segregation of so-called antisite atoms in CoAl(100)
and will be shortly discussed at the end of the talk.
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