Heterogeneity of the local structure in sub- and supercritical ammonia: a voronoi polyhedra analysis

A. Idrissi, I. Vyalov, M. Kiselev, M. V. Fedorov, P. Jedlovszky

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

We report results of molecular dynamics simulations and detailed analysis of the local structure of sub- and supercritical ammonia in the range of temperature between 250 and 500 K along the 135 bar isobar. This analysis is based on the behavior of distributions of metric and topological properties of the Voronoi polyhedra (VP). We show that by increasing the temperature, the volume, surface, and face area distributions of the Voronoi polyhedra as well as the vacancy radius distribution broaden, particularly near the temperature T-alpha, where the calculated thermal expansion coefficient has its maximum. Furthermore, the rate of increase of the corresponding mean values and fluctuations increases drastically when approaching T-alpha. This behavior clearly indicates that the local structure, as described by the VP, becomes increasingly heterogeneous upon approaching this temperature. This heterogeneous distribution of ammonia molecules is traced back to the increase of the large voids with increasing temperature, and is also clearly seen in the behavior of the fluctuation of the local density, as measured by the VP. More interestingly, the maximum in the heterogeneity coincides with the maximum of the fluctuation in the density of the VP.

LanguageEnglish
Pages9646-9652
Number of pages7
JournalJournal of Physical Chemistry B
Volume115
Issue number31
DOIs
Publication statusPublished - 11 Aug 2011

Fingerprint

polyhedrons
Ammonia
ammonia
Temperature
temperature
isobars
Vacancies
Thermal expansion
Molecular dynamics
voids
thermal expansion
molecular dynamics
Molecules
radii
Computer simulation
coefficients
molecules
simulation

Keywords

  • molecular dynamics
  • free volume
  • liquid water
  • computer simulation
  • random packings
  • AB-initio
  • tessellation
  • spheres
  • transition
  • particles
  • TIC - Bionanotechnology

Cite this

Idrissi, A. ; Vyalov, I. ; Kiselev, M. ; Fedorov, M. V. ; Jedlovszky, P. / Heterogeneity of the local structure in sub- and supercritical ammonia : a voronoi polyhedra analysis. In: Journal of Physical Chemistry B. 2011 ; Vol. 115, No. 31. pp. 9646-9652.
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Heterogeneity of the local structure in sub- and supercritical ammonia : a voronoi polyhedra analysis. / Idrissi, A.; Vyalov, I.; Kiselev, M.; Fedorov, M. V.; Jedlovszky, P.

In: Journal of Physical Chemistry B, Vol. 115, No. 31, 11.08.2011, p. 9646-9652.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Heterogeneity of the local structure in sub- and supercritical ammonia

T2 - Journal of Physical Chemistry B

AU - Idrissi, A.

AU - Vyalov, I.

AU - Kiselev, M.

AU - Fedorov, M. V.

AU - Jedlovszky, P.

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AB - We report results of molecular dynamics simulations and detailed analysis of the local structure of sub- and supercritical ammonia in the range of temperature between 250 and 500 K along the 135 bar isobar. This analysis is based on the behavior of distributions of metric and topological properties of the Voronoi polyhedra (VP). We show that by increasing the temperature, the volume, surface, and face area distributions of the Voronoi polyhedra as well as the vacancy radius distribution broaden, particularly near the temperature T-alpha, where the calculated thermal expansion coefficient has its maximum. Furthermore, the rate of increase of the corresponding mean values and fluctuations increases drastically when approaching T-alpha. This behavior clearly indicates that the local structure, as described by the VP, becomes increasingly heterogeneous upon approaching this temperature. This heterogeneous distribution of ammonia molecules is traced back to the increase of the large voids with increasing temperature, and is also clearly seen in the behavior of the fluctuation of the local density, as measured by the VP. More interestingly, the maximum in the heterogeneity coincides with the maximum of the fluctuation in the density of the VP.

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