Structure and dynamics of liquid selenium

Abstract

First-principles molecular-dynamics simulations of liquid selenium at the temperatures 570, 870, and 1370 K are presented. It is shown that calculations based on the local-density approximation are not satisfactory, because they seriously overestimate the equilibrium density of the solid and the liquid, and they give only rough agreement with measured structural data when the liquid is simulated at the experimental density. The inclusion of gradient corrections mitigates these problems, and most of the results presented are based on the generalized gradient approximation. The simulations are used to investigate the three-dimensional structure of the liquid, and results are presented for the bond-angle and dihedral-angle distributions, the concentration and structure of different Se n rings, and the temperature-dependent length of chains. The self-diffusion constants and vibrational spectra are shown to agree satisfactorily with experimental data, and an analysis of the lifetime of covalent bonds gives insight into the diffusion mechanism. The electronic density of states of the liquid displays all the features known for the solid, and this indicates that the electronic structure changes little on melting.

Microscopic structure and dynamics of molten Se50Te50 alloys

“…This latter value is somewhat smaller than that the estimated experimental value in molten elemental Te ͑Ϸ100°, close to the value in the solid which is known to be preserved upon melting 29 ͒. As to the bond angle XSeŶ whose distribution peaks around 100°, is somewhat lower than the experimental and ab initio values 30 found in molten Se ͑Ϸ110°͒. It seems that the accurate ab initio description of Se atoms somewhat compensates the deficiencies in the treatment of Te atoms ͑note that the stability of the cubic structure is overestimated 28 in the DFT for Te and this tends to favor bond angles close to 90°͒ as found in Ref.…”

“…In particular, the fact that increasing temperature induces a semiconductor/metal transition has motivated numerous experimental and theoretical investigations. [1][2][3][4][5][6] In the case of alloys, this transition can also be tuned by changes in the composition, a feature that makes this system even more attractive from the technological point of view. However, despite the growing number of works concerned with the properties of elemental Se and Te, relatively few investigations have focused on the behavior of SeTe alloys.…”

Experimental techniques of high-resolution inelastic X-ray scattering measurements for supercritical metallic fluids at high temperature and high pressure using synchrotron radiation at SPring-8

“…Secondly, the transition promotes the increase of very short chains and it seems to be correlated with the instability of the chain structure. Recent molecular dynamics simulations [31][32][33] have clarified the microscopic structure in the SC-M transition in the expanded fluid Se. However, there remains a question why the volume tends to contract in the SC-M transition, because the simulation assumed the temperature dependence of the density experimentally determined.…”

First-principle molecular dynamics study of the structural and electronic properties of liquid and amorphous Ni–Al alloys

“…The VASP code makes use of ultrasoft pseudopotentials [18], and an expansion of the electronic wave functions in plane waves. The approach has been applied widely in AIMD simulations of liquid metals and alloys [19][20][21][22][23][24][25][26][27]. Our simulations were performed using a cubic supercell containing 128 particles with periodic boundary conditions and C-points sampling.…”