  The low-index surfaces of Au and Pt all tend to reconstruct, a fact that is
of key importance in many nanostructure, catalytic, and electrochemical
applications. Remarkably, some significant questions regarding their structural
energies remain even today, in particular for the large-scale quasihexagonal
reconstructed (100) surfaces: Rather dissimilar reconstruction energies for Au
and Pt in available experiments, and experiment and theory do not match for Pt.
We here show by all-electron density-functional theory that only large enough
"(5 x N)" approximant supercells capture the qualitative reconstruction energy
trend between Au(100) and Pt(100), in contrast to what is often done in the
theoretical literature. Their magnitudes are then in fact similar, and closer
to the measured value for Pt(100); our calculations achieve excellent agreement
with known geometric characteristics and provide direct evidence for the
electronic reconstruction driving force.
