High-Pressure Phases and Spectral Properties of Silicon
Reetam Paul, Valentin V. Karasiev, Suxing Hu
Laboratory for Laser Energetics, University of Rochester, Rochester, NY 14623-1299
By utilizing a combination of density functional theory, quantum molecular dynamics, and lattice dynamics, we have computed the phase diagram of silicon up to a pressure of 4 TPa. Upon introducing anharmonic corrections based on an averaged approach1 to quasiharmonic phonon calculations, a substantial change in phase boundaries was observed. This was more evident in case of the orthorhombic phases of Imma and Cmce-16. Consequently, we used molecular dynamics with a canonical ensemble to calculate the melt curve, and proceeded on to use phonon quasiparticle-based anharmonic calculations2 to predict the absorption and scattering spectra of relevant phases along isochores to establish an additional signature of melting. The most important finding of this work pertains to the prediction of a sequence of face-centered cubic (fcc) to body-centered cubic (bcc) to simple cubic (sc) phase transitions at multi-TPa pressures, which implies a reduction in coordination number. The reasons for such anomalous transitions have also been investigated.
This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority.
1 S. G. Moustafa, A. J. Schultz, E. Zurek, and D. A. Kofke, Phys. Rev. B 96, 014117 (2017).
2 A. Carreras, A. Togo, and I. Tanaka, Comput. Phys. Commun. 221, 221 (2017).