Carleo G, Moroni S, Baroni S

The lattice dynamics of hcp crystalline He-4 is studied at zero temperature and for two different densities (near and far from melting), using a ground-state path-integral quantum Monte Carlo technique. The complete phonon dispersion is obtained, with particular attention to the separation of optic and acoustic branches and to the identification of transverse modes. Our study also sheds light on the residual coherence affecting quasiparticle excitations in the intermediate momentum region, in between the phonon and nearly free-particle regimes.