Structural transformation between long and short-chain form of liquid sulfur from ab initio molecular dynamics

Abstract

We present results of ab initio molecular dynamics study of the structural transformation occurring in hot liquid sulfur under high pressure, which corresponds to the recently observed chain-breakage phenomenon and to the electronic transition reported earlier. The transformation is temperature-induced and separates two distinct polymeric forms of liquid sulfur: high-temperature form composed of short chain-like fragments with open endings and low-temperature form with very long chains. We offer a structural description of the two liquid forms in terms of chain lengths, cross-linking, and chain geometry and investigate several physical properties. We conclude that the transformation is accompanied by changes in energy (but not density) as well as in diffusion coefficient and electronic properties—semiconductor-metal transition. We also describe the analogy of the investigated process to similar phenomena that take place in two other chalcogens selenium and tellurium. Finally, we remark that the behavior of heated liquid sulfur at ambient pressure might indicate a possible existence of a critical point in the low-pressure region of sulfur phase diagram.

First-principles simulations of glass-formers

“…This approach allows thus to give a correct dynamics but this at the cost of a increased computational load. Only in the last few years the numerical algorithms have been improved to such an extent that today it is possible to simulate within BOMD several hundreds particles [17][18][19][20]. The brief description of the ab initio simulations that we have given so far should make it clear that in practice the computer code to carry out such simulations must be extremely optimized in order to keep the necessary computer time for the simulations within a reasonable limit.…”

Liquid–liquid transition and critical point in sulfur

“…An experimental study 24 suggested the existence above 6 GPa of a purely polymeric liquid composed of long chains below 1000 K, which split to shorter chains at higher temperature. Ab-initio molecular dynamics simulations 25 reproduced this chain breakage in the compressed liquid but found no discontinuous change of density associated to this process. So far, no in-situ structural or vibrational studies have been conducted in the pressure region below 3 GPa in the mixed molecular-polymeric liquid.…”

Elemental sulphur in the synthesis of sulphur-containing polymers: reaction mechanisms and green prospects

“…It has been reliably characterised using quantum chemistry calculations. [80][81][82] The S 8 conformation includes structures such as C 2 (endo-exo ring), C 2 (twisted ring), D 2d (boat), C 2h (chair), C 2 (cluster), C 1 (S 7 ]S), and C 1 (S 7 ]S eq ), as well as a few branched and unbranched forms. The crown-shaped S 8 octatomic conformation (D 4d ) has been conrmed to be a global energy minimum using various levels of theory.…”