Fine structure of spatial distribution functions of water oxygen atoms according to quantum-chemical calculation data

The currently used radial distribution functions (pair correlation of particles) are time- and space-averaged quantities, and reconstructing the size and structure of individual molecular groups of liquids from them cannot be solved unambiguously. In the article, using liquid water under normal conditions as an example, it is shown that its structure is best represented by the instantaneous spatial distribution of oxygen atoms over distances. This distribution was calculated from the structure of a water cluster (H2O)56 without taking into account molecules subject to the edge effect. The cluster structure was calculated by the nonempirical quantum chemical method in the HF LCAO approximation with the 6-31G basis set. The data on the exact positions of each oxygen atom of several molecules located near the cluster center were selected as the origin of coordinates for calculating the radial distribution function g(r) in the usual way. The shape of g(r) strongly depends on the integration step. With a minimum integration step of 0,1 Å at r < 5.6 Å, it has 10 peaks, the number of which decreases to three with its increase. In this case, the g(r) diagram acquires a normal form, and information about its fine structure is lost. The most reliable and visual interpretation can be obtained by jointly analyzing the radial distribution diagram of the number density of particles and the spatial distribution of particles by distances.