Rotational Phase Transition and Melting in a Two-Dimensional Hard-Cyclic-Tetramer System

Abstract

Mechanical simulations of a two-dimensional system of N cyclic tetramers, studied in square (N = 289) and hexagonal (N~ 331) boxes, demonstrate the existence of crystalline (d = V/V^> 1.14; different structures are observed), rotator {l,lS%d ^1.29), and fluid {d^ 1.31) phases (V 0 is the area of the box with close-packed structure). Observed phase coexistences suggest first-order transitions.

Negative Poisson’s ratio of two-dimensional hard cyclic tetramers

“…Systems created by multimer molecules present rich phase diagrams which have been studied using both mechanical [48][49][50] and computer simulations [51][52][53][54][55]. The phase behavior of such models are useful for the classification of phase transitions because clear evidence of structural and orientational transitions can be easily observed.…”

Poisson’s ratio of orientationally disordered hard dumbbell crystal in three dimensions

“…The hard sphere system [8,9], which provided a good insight into physics underlying the freezing of rare gases [10,11], is probably the most widely known example. Monte Carlo (MC) simulations of anisotropic hard-body systems have shown that they are able to mimic various liquid-crystalline and solid phases [12][13][14][15][16][17][18][19][20][21][22]. In particular, it was shown [23][24][25][26] that a crude model of a diatomic molecule, the hard homonuclear dumbbell -formed by two fused spheres, each of diameter r, with centers separated by distance d -can form the above-mentioned rotator phase besides the fluid and the fully-ordered crystalline phases.…”

The free energy of hard dimer solids revisited

“…The hard sphere model system [1,2] has made the freezing of rare gases significantly less obscure [3,4]. Simulations of hard ellipsoids [5][6][7], hard spherocylinders [8,9] and hard cyclic multimers [10], revealing a variety of liquid-crystalline and solid phases, have shown that even complex phenomena (such as phase transitions) may be purely geometrical in origin.…”