The local structure of various hydrogen bonded liquids: Voronoi polyhedra analysis of water, methanol, and HF

The local structure of three hydrogen bonded liquids comprising clusters of markedly different topology: water, methanol, and HF are investigated by a nalyzing the properties of the Voronoi polyhedra (VP) of the molecules in c onfigurations obtained from Monte Carlo computer simulations. For compariso ns, the properties of argon as a nonassociating reference liquid are also c alculated. It is found that in liquid HF the fluctuation of the local densi ty is much larger than in the other three liquids, and hence, besides the d ense regions, this liquid contains numerous large voids as well. The size o f the largest of these voids is found to be commensurate with a cluster of 11 HF molecules, whereas the number of voids as large as one molecule is in the order of the number of molecules. It is found that the number of the h ydrogen-bonded neighbors of the HF molecules located at the boundary of suc h voids does not differ considerably from that of the other molecules, and thus they do not have any specific topological position (e.g., chain termin al) in the hydrogen bonded chains of the molecules. The shape of the VP is found to reflect the arrangement of the nearest neighbors of the molecules. Thus, the VP are considerably less spherical and their topological propert ies are distributed in a wider range in the associated liquids than in argo n. Similarly, in the hydrogen bonded liquids considerably more geometric ne ighbors are found than the number of molecules belonging to the first coord ination shell. On the other hand, in liquid argon, which is a closely packe d system, the two values are found to be close to each other. The inhomogen eities of the local density of liquid HF are also reflected in the shape of the VP. The molecules located at the boundary of the large voids are found to have more spherical VP with more and larger faces than the other ones. (C) 2000 American Institute of Physics. [S0021-9606(00)51044-7].