Near-Equilibrium Ordering of the Crystalline Phases of Atomic Hydrogen

摘要

Some time ago Min found the near-equilibrium sequence of phases of paramagneticcrystalline H to be (in order of increasing energy) simple cubic (SC), hexagonal close packed (HCP), body-centered cubic (BCC), and face-centered cubic (FCC), with FCC and HCP substantially separated (about 60 mRy/atom). This result is counterintuitive on three counts when compared with crystalline Li. That comparison suggests that HCP should lie only slightly below FCC and both should be substantially below BCC. (Simple cubic should lie lowest in H but not in Li because of the difference in orbital occupancy.) We have redone the calculations with our published full-potential linearized augmented plane wave code WIEN. We find the sequence of phases with increasing energy to be SC, HCP, FCC, and BCC, the ordering expected from solid Li. By direct exploration of dense k-space meshes, we show that the difference in predictions results from a K-space mesh extrapolation technique used by Min.