Phase diagram of argon clusters

Heterophasic oscillations in nanoscale systems

Both the energy differences between metastable and stable phases and the energy barriers separating these phases decrease with decreasing particle number. Then, for small enough systems, random heterophasic fluctuations of the entire system become an observable form of thermal motion. We discuss mechanisms and observation conditions for these random transitions between phases.

Monte Carlo simulation in the isobaric-multithermal ensemble of a bulk Lennard-Jones fluid system: thermodynamic quantities for pressure from P{ *}=2.42 to 7.25

A Monte Carlo (MC) simulation in the isobaric-multithermal (MuTh) ensemble has been carried out for a bulk Lennard-Jones fluid system that consists of 108 particles. The MuTh weight factor which we determined turned out to be reliable for the temperature and pressure range from (T{ *},P{ *})=(T_{0}{ *},P_{0}{ *})=(2.09,7.25) to (T{ *},P{ *})=(0.417,1.45) along P{ *}/T{ *}=P_{0}{ *}/T_{0}{ *} . Thermodynamic quantities calculated from the MuTh MC production run by the reweighting techniques showed the discontinuous change, which is the feature of the first-order phase transition. The radial distribution functions suggest that the transition takes place between liquid and solid states. Two distinct local maxima were observed in the obtained contour representations of the probability distribution at T{ *}=1.04 and P{ *}=3.63 , which is the phase transition point along P{ *}/T{ *}=P_{0}{ *}/T_{0}{ *} .

Shape effect of hot droplets on fragmentation

Fragmentation dynamics and the shape effect of initial hot droplets on it are investigated by using a classical molecular dynamics method. As the initial conditions for the fragmentation simulation, small hot droplets in the supercritical phase, with the number of particles N less than approximately 10(3), are considered. It is revealed that, in the process of the fragmentation, the largest cluster approaches a certain quasistable state corresponding to the so-called triple point. It is also revealed that the initial shape of the hot droplets has a significant effect on the cluster distribution generated after fragmentation; i.e., the more prolate the initial shape, the more markedly the size of the largest cluster decreases and the number of small clusters increases. The shape effect diminishes with an increasing number of particles in the initial hot droplet and could be negligible for large hot droplets, of the number of particles N more than approximately 10(3).

New approach to the first-order phase transition of Lennard-Jones fluids

The multicanonical Monte Carlo method is applied to a bulk Lennard-Jones fluid system to investigate the liquid-solid phase transition. We take the example of a system of 108 argon particles. The multicanonical weight factor we determined turned out to be reliable for the energy range between -7.0 and -4.0 kJ/mol, which corresponds to the temperature range between 60 and 250 K. The expectation values of the thermodynamic quantities obtained from the multicanonical production run by the reweighting techniques exhibit the characteristics of first-order phase transitions between liquid and solid states around 150 K. The present study reveals that the multicanonical algorithm is particularly suitable for analyzing the transition state of the first-order phase transition in detail.