At present, computer simulation is one of the most effective research methods in any scientific field, including chemistry. This method can be used when planning future experiments or in cases where direct study of the object is problematic. In addition, computational models are becoming an important complement to experimental research. In this regard, computer modelling is becoming an integral part of modern water research, the purpose of which is to explain its numerous anomalies. In this article we will discuss several iconic examples of such studies.
Rudolph Pariser in front of a blackboard full of quantum calculations, contemplating a molecular model, 1950s. ELISE communications / The Hagley Museum and Library
The American scientist Gaiduk presented a dielectric-dependent hybrid functional in his work. The functional is a mathematical apparatus with particular equations and functions for theoretical calculations. It can provide a fairly accurate description of the structure of water, as well as various types of bonds present in it. It was found that the dielectric-dependent hybrid functional can also be used to describe the vibration and dielectric properties of liquid water. One can use it to predict a realistic structure of water at a temperature of 311 K (38ºС).
Another example is the work of the American scientist Piskulich. He proposed a combined functional that allows factors such as temperature and system pressure to be taken into account when describing the structure of water. The author applied this method to the calculation of the volumes of water at which self-diffusion of water (its spontaneous diffusion) is activated. The findings correlate with experimental data from previous studies. This method, according to Piskulich, should be widely used in studies of the properties of water.
Computer simulation of the structure of fullerene
Often the need to analyse certain data with the help of computer simulation arises during the experiment. Such a decision, for example, was made by the English scientist Chen after he and his team recorded an increase in water consumption when passing it through graphene channels. Thanks to a computer simulation, the connection between the structure of water and the change in flow in rectangular carbon nanotubes was first discovered. Chen attributed the significant increase in the rate of flow (in comparison with the classical dynamics of the Poiseuille flow) to the formation of layered two-dimensional water molecule structures in a limited space. The structures were preserved up to a specific channel height (2.38 nm or six layers of graphene) and were a complex crystal that had not previously been observed. It transpired that the structure of water changed significantly due to the retention of the graphene channel walls (the so-called 'locked in' water) and acquired properties different from the properties of water in the free volume. In particular, the flow rate of the 'locked in' water significantly depended on the shape and size of the nano-scale channel in which it flowed. A new form of ice was also discovered that is absent from the normal phase diagram. The properties of limited water structures are important for understanding the transport property mechanisms of channels in living organisms.
Computer model of liposome
An interesting use of computational models is in the study of processes occurring near phospholipid (cell) membranes. In his study, the American scientist Martelli examined the structure of water molecules sandwiched between two membranes. Each membrane is made of two lipid layers. Changes in the structure formation of water molecules were observed in areas close to the oscillating lipid surfaces. The surface interface influenced the density and structure of the water, which in turn was accompanied by changes in the dynamic behaviour of limited water (located between hydrophobic membranes). The observed effect is small, but significant. The author expects that it will be possible to observe a similar orderliness when water comes into contact with other hydrophobic surfaces. It was concluded that the membrane surface has a structural effect that extends further than had been indicated in earlier studies. This fact should be taken into account when analysing experimental data about water bounded by membranes, and it can perhaps help us to understand the role of water in biological systems.
The Greek scientist Oikonomou has also utilised computer simulation in his research. He is engaged in the study of highly diluted solutions. The author of the article notes that in such solutions, molecules of the original substance affect the solvent molecules. As a result, aggregates of solvent molecules are formed. These aggregates can, in turn, change some physical properties (in this article, viscosity) of highly diluted systems, which affects the process of molecules' movement in a liquid.
The aforementioned works testify to the successful application of computer modeling in studying the properties of water and its role in life processes. Of course, we are still far from fully understanding all aspects of the structure of water. However, the new opportunities that computer modelling opens up for further research into this amazing substance are already manifesting themselves.