### 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.

Language | English |
---|---|

Pages | 9646-9652 |

Number of pages | 7 |

Journal | Journal of Physical Chemistry B |

Volume | 115 |

Issue number | 31 |

DOIs | |

Publication status | Published - 11 Aug 2011 |

### Fingerprint

### Keywords

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

### Cite this

*Journal of Physical Chemistry B*,

*115*(31), 9646-9652. https://doi.org/10.1021/jp204078u

}

*Journal of Physical Chemistry B*, vol. 115, no. 31, pp. 9646-9652. https://doi.org/10.1021/jp204078u

**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.

Research output: Contribution to journal › Article

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.

PY - 2011/8/11

Y1 - 2011/8/11

N2 - 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.

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.

KW - molecular dynamics

KW - free volume

KW - liquid water

KW - computer simulation

KW - random packings

KW - AB-initio

KW - tessellation

KW - spheres

KW - transition

KW - particles

KW - TIC - Bionanotechnology

U2 - 10.1021/jp204078u

DO - 10.1021/jp204078u

M3 - Article

VL - 115

SP - 9646

EP - 9652

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 31

ER -