A new approach for estimating the density of liquids

J. Phys.: Condens. Matter

Sakagami

Kohara

et al. 2016

A molecular liquid GeI4 is a candidate that undergoes a pressure-induced liquid-to-liquid phase transition. This study establishes the reference structure of the low-pressure liquid phase. Synchrotron x-ray diffraction measurements were carried out at several temperatures between the melting and the boiling points under ambient pressure. The molecule has regular tetrahedral symmetry, and the intramolecular Ge-I length of 2.51 Å is almost temperature-independent within the measured range. A reverse Monte Carlo (RMC) analysis is employed to find that the distribution of molecular centers remains self-similar against heating, and thus justifying the length-scaling method adopted in determining the density. The RMC analysis also reveals that the vertex-to-face orientation of the nearest molecules are not straightly aligned, but are inclined at about 20 degrees, thereby making the closest intermolecular I-I distance definitely shorter than the intramolecular one. The prepeak observed at ∼1 Å(-1) in the structural factor slightly shifts and increases in height with increasing temperature. The origin of the prepeak is clearly identified to be traces of the 111 diffraction peak in the crystalline state. The prepeak, assuming the residual spatial correlation between germanium sites in the densest direction, thus shifts toward lower wavenumbers with thermal expansion. The aspect that a relative reduction in molecular size associated with the volume expansion is responsible for the increase in the prepeak's height is confirmed by a simulation, in which the molecular size is changed.

“…(The rather small number of molecules employed is to quantitatively compare the results with those for SnI 4 previously examined. This comparison will be discussed in [20]. )…”

Section: Methods Of Analysismentioning

confidence: 94%

Section: Methods Of Analysismentioning

confidence: 99%

Section: Methods Of Analysismentioning

confidence: 99%

Section: Origin Of the Prepeakmentioning

confidence: 99%

See 2 more Smart Citations

Structure of a molecular liquid GeI₄

J. Phys.: Condens. Matter

Sakagami

Kohara

et al. 2016

“…The cubic system with periodic boundary conditions was used as is. Based on the length-scaling method [23], the density of the liquid was evaluated by adjusting the size of a cubic cell employed by the MD simulation so that the position of the prepeak of the MD-based structure factor coincides with that of the experimental structure factor. The adjusted length of a side of the cell along with the number density is listed in table 1.…”

Section: Rmcmentioning

confidence: 99%

Does a network structure exist in molecular liquid SnI₄and GeI₄?

Sakagami

J. Phys.: Condens. Matter

2017

The existence of a network structure consisting of electrically neutral tetrahedral molecules in liquid SnI and GeI at ambient pressure was examined. The liquid structures employed for the examination were obtained from a reverse Monte Carlo analysis. The structures were physically interpreted by introducing an appropriate intermolecular interaction. A 'bond' was then defined as an intermolecular connection that minimizes the energy of intermolecular interaction. However, their 'bond' energy is too weak for the 'bond' and the resulting network structure to be defined statically. The vertex-to-edge orientation between the nearest molecules is so ubiquitous that almost all of the molecules in the system can take part in the network, which is reflected in the appearance of a prepeak in the structure factor.

Pressure-induced local symmetry breaking upon liquid–liquid transition of GeI4 and SnI4

The Journal of Chemical Physics

Sakagami²,

Iwayama

2019

SnI4 and GeI4 have been confirmed to have another liquid state appearing on compression. To identify the microscopic pathway from the low- to high-pressure liquid states, the structure of these liquids in the appropriate thermodynamic regions was analyzed using a reverse Monte Carlo method. The occurrence of pressure-induced symmetry lowering of molecules, from regular tetrahedral to ammonia-like pyramidal symmetry, was then recognizable in these systems. This symmetry lowering is reflected in the change in shape of the molecular form factor. The latter change occurs abruptly near the expected transition pressure in liquid SnI4, whereas it proceeds gradually in GeI4. This is consistent with our observation that SnI4 seems to undergo a first-order liquid–liquid transition, whereas the transition seems to end up with a crossover in liquid GeI4. Interestingly, when the molecular density becomes high, it is possible for the two-body intermolecular interaction to have a double-minimum character, which offers two characteristic length scales corresponding to two liquid states with different densities. However, quantum chemical calculations show that molecular deformation for this type of symmetry lowering results in an increase in electronic energy, which leaves the problem of the physical origin for this anisotropic deformation. We speculate that this symmetry lowering occurs as a precursor to the whole change in the liquid structure.