Thermodynamics of water clusters under high pressures. A case study for (H2O)15 and (H2O)15CH4

Abstract

Thermal properties and structures of the water cluster containing fifteen molecules, either pure or doped with methane, are studied via classical parallel tempering Monte Carlo calculations in the isothermal-isobaric ensemble. The main emphasis is on structural transformations the cluster undergoes with increasing temperature and pressure. A simple TIP4P interaction model is employed for water and the unified-atom approximation with a Lennard-Jones potential is used to model the methane-water interaction. The results are compared with the data obtained recently for zero temperature via evolutionary algorithm calculations [Hartke, J. Chem. Phys., 2009, 130 art. no. 024905].

Finite Systems under Pressure: Assessing Volume Definition Models from Parallel-Tempering Monte Carlo Simulations

“…}, for accepting or rejecting translation, rotation, and volume moves. 45 For the second and third groups of methods (M3-M6 volume models), based on the direct computation of system volume, we rewrite Eq. 1 as follows:…”

“…Water clusters have been extensively studied by both theory and experiment, 45,[51][52][53][54][55][56][57][58][59] and considerable insight has been gained on lower-energy structures as a function of the cluster size, classified into two broad categories, such as 2-D (ring or chain) structures and 3-D (cage, prism, or cube and so on) structures. 60 However, there is still a considerable lack of understanding of the transitions from properties and structures of small-, intermediate-sized clusters to those of the large-sized clusters.…”

“…Through the MC configurations' sampling, the employed volume model could directly affect the formation of specific isomeric structures, especially under high pressures, so we have emphasized the need to test and check the effect of volume models on thermodynamic properties of specific cluster systems. 32,34,[44][45][46][47] The goal of our work is to undertake a general investigation of the effects of pressure on cluster structures. Since the probability of sampling cluster's configuration space is governed, under NPT conditions, by the enthalpy, H = E (int) + P V , the P V term may become important at high pressures.…”

A thermodynamic view on the microsolvation of ions by rare gas: application to Li+ with argon

“…These problems are minimized with the use of extended ensemble techniques, such as parallel tempering Monte Carlo (PTMC), which uses several replicas at different temperatures to build a new ensemble where attempts to exchange between replicas at different temperatures are performed. Although PTMC methodology has been applied to study several atomic and molecular clusters [14][15][16][17][18][19][20][21][22][23][24][25] , to the best of our knowledge, its use with microsolvation systems is very scarce and limited to model solvents 26,27 .…”

Photoabsorption markers of pressure-induced phase changes in small mercury clusters. A case study on Hg8

“…Alternatively, structural changes can be achieved by varying the external pressure the studied system is exposed to if metastable isomers are more compact than the stable one. 3,4 The phase changes can be identied by inspecting temperature and/or pressure dependences of specic properties of the system which are directly or indirectly sensitive to changes of the layout of atoms of the system in space. For example, internal energy (enthalpy), heat capacity, correlations between various quantities (like the Pearson coefficient for the energy and the system volume 3 ), and Lindemann index 5 are used to pinpoint regions on the temperature and/or pressure scales where the phase changes take place (so called coexistence regions since various structural motifs coexist during a particular phase change 1,2 ).…”