We describe the formalism, as well as numerical and implementation issues behind PARSEC -the pseudopotential algorithm for real-space electronic structure calculations. Its current capabilities are illustrated via application of PARSEC to numerous problems in nanoscience.

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In first-principles variable-cell-shape molecular dynamics simulations and structural optimizations of nitrogen at pressures of 0-500 GPa, the phase with lowest enthalpy at high pressures, BP, was found to transform at low pressures into a new, metastable, metallic phase with a chainlike structure. The latter may possibly be related to a metastable nonmolecular phase that was recently observed experimentally at low temperatures and pressures.

The evolution of the magnetic moment in iron clusters containing 20 to 400 atoms is investigated using first-principles numerical calculations based on density-functional theory and real-space pseudopotentials. Three families of clusters are studied, characterized by the arrangement of atoms: icosahedral, body-centered cubic centered on an atom site, and body-centered cubic centered on the bridge between two neighboring atoms. We find an overall decrease of magnetic moment as the clusters grow in size towards the bulk limit. Clusters with faceted surfaces are predicted to have magnetic moment lower than other clusters with similar size. As a result, the magnetic moment is observed to decrease as function of size in a non-monotonic manner, which explains measurements performed at low temperatures.

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