The phase transition of ZnS from the zincblende (ZB) structure to the rocksalt (RS) structure is investigated by the ab initio plane-wave pseudopotential density functional theory method. It is found that the pressures for transition from the ZB structure to the RS structure are 17.5 GPa from total energy–volume data and 15.4 GPa from equal enthalpies, consistent with the experimental data. From the high pressure elastic constants obtained, we find that the ZB structure ZnS is unstable when the applied pressure is larger than 17 GPa. Moreover, the dependence of the normalized primitive cell volume V/V0 on pressure P can also be successfully obtained.

We calculated the phase transition, elastic constants, full phonon dispersion curves, and thermal properties of molybdenum (Mo) for a wide range of pressures using density functional theory. Mo is stable in the bodycentered-cubic (bcc) structure up to 703 (19 GPa and then transforms to the face-centered close-packed (fcc) structure at zero temperature. Under high temperature and pressure, the fcc phase of Mo is more stable than the bcc phase. The calculated phonon dispersion curves accord excellently with experiments. Under pressure, we captured a large softening along H-P in the TA branches. When the volume is compressed to 7.69 A3, the frequencies along H-P in the TA branches soften to imaginary frequencies, indicating a structural instability. When the pressure increases, the phonon calculations on the fcc Mo predict the stability by promoting the frequencies along Γ to X and Γ to L symmetry lines from imaginary to real. The thermal equation of state was also investigated. From the thermal expansion coefficient and the heat capacity, we found that the quasiharmonic approximation was valid only up to about melting point at zero pressure. However, under pressure, the validity can be extended to a much higher temperature.

Absorption spectra for small sulfur clusters Sn (n = 2-8) are calculated using an adiabatic time-dependent density-functional formalismwithin the local density approximation (LDA). We compare the calculated spectra with those calculated using the simple LDA approach. The calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations. In addition, we also obtain a significant threshold absorption, which can distinguish different ground states of the sulfur clusters.

We have investigated the structures and the elastic constants of hcp MgB2 at high pressures using the full-potential linearized muffin-tin orbital (FP-LMTO) scheme within the generalized gradient approximation correction (GGA) in the frame of density functional theory (DFT). The obtained normalized volume dependence of the resulting pressure is in excellent agreement with experiment. The elastic constants and acoustic anisotropy as a function of the applied pressure are presented. An analysis for the calculated parameters has been made to reveal the anisotropy of MgB2.

We apply a finite-difference pseudopotential density functional theory in real space and the Langevin molecular dynamics annealing technique as well as the adiabatic time-dependent density functional theory within the local density approximation (TDLDA) to the descriptions of structures and optical absorption spectra of carbon clusters C8. It is shown that the odd-numbered clusters have the linear structures and most of the even-numbered clusters prefer cyclic structures. The calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations.

We report a detailed first-principles calculation to investigate the structures, elastic constants, and phase transition of Ti. The axial ratios of both a-Ti and w-Ti are nearly constant under hydrostatic compression, which confirms the latest experimental results. From the high pressure elastic constants, we find that the a-Ti is unstable when the applied pressures are larger than 24.2 GPa, but the w-Ti is mechanically stable at all range of calculated pressure. The calculated phonon dispersion curves agree well with experiments. Under compression, we captured a large softening around point of w-Ti. When the pressure is raised to 35.9 GPa, the frequencies around the point along-M-K and -A in transverse acoustical branches become imaginary, indicating a structural instability. Within quasiharmonic approximation, we obtained the full phase diagram and accurate thermal equations of state of Ti. The phase transition w-Ti→a-Ti→b-Ti at zero pressure occurs at 146K and 1143K, respectively. The predicted triple point is at 9.78 GPa, 931 K, which is close to the experimental data. Our thermal equations of state confirm the available experimental results and are extended to a wider pressure and temperature range.