The complexity of first-principles total energy calculations limits the pool of structure types considered for a ground-state search for a binary alloy system to a rather small, $O\left(10\right)$, group of “usual suspects.” We conducted an unbiased search of fcc-based ${\mathrm{Ag}}_{1-x}{\mathrm{Pd}}_x$ structures consisting of up to many thousand atoms by using a mixed-space cluster expansion. We find an unsuspected ground state at $50\%-50\%$ composition—the ${L1\mathrm{}}_1$ structure, currently known in binary metallurgy only for the ${\mathrm{Cu}}_{0.5}{\mathrm{Pt}}_{0.5}$ alloy system. We also provide predicted short-range-order profiles and mixing enthalpies for the high temperature, disordered alloy.

• Received 13 February 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.165502