Distribution of hydrogen-bonded rings in pure liquid water and methane solution by a Monte Carlo method

Abstract Monte Carlo method was used to examine the distributions of non-short-circuited rings of hydrogen-bonded molecules in TIP4P water and methane solution at five temperatures ranging from −25 to 75°C. Our interest was the distributions of water pentamers and hexamers in TIP4P water and methane solution. Therefore, the polygons larger than water hexamer were not considered. In counting the hydrogen-bonded rings, a energetic definition of the hydrogen bond was used. It was found that the ratio of water hexamers and pentamers (R 6 /R 5 ) increased in according to decreasing temperature in both pure liquid water and methane solution; the decrease of temperature makes the forming of water hexamers easier than that of water pentamers. And also, at same temperature, the R 6 /R 5 's value in methane solution was greater than that in pure liquid water. This implies that, in methane solution, water hexamers are formed more easily than water pentamers, in comparing with pure liquid water On the other hand, at high temperature, the average numbers of water pentamers and hexamers are greater in pure liquid water than in methane solution, whereas reverse at low temperature. That is, at high temperature, a methane molecule induces the breaking of water pentamers and hexamers, whereas at low temperature, the forming of those water polygons.