Structure of the simple harmonic-repulsive system in liquid and glassy states studied by the triple correlation function

Abstract

An efficient description of the structures of liquids and, in particular, the structural changes that happen with liquids on supercooling remains to be a challenge. The systems composed of soft particles are especially interesting in this context because they often demonstrate non-trivial local orders that do not allow to introduce the concept of the nearest-neighbor shell. For this reason, the use of some methods, developed for the structure analysis of atomic liquids, is questionable for the soft-particle systems. Here we report about our investigations of the structure of the simple harmonic-repulsive liquid in 3D using the triple correlation function (TCF), i.e., the method that does not rely on the nearest neighbor concept. The liquid is considered at reduced pressure (P = 1.8) at which it exhibits remarkable stability against crystallization on cooling. It is demonstrated that the TCF allows addressing the development of the orientational correlations in the structures that do not allow drawing definite conclusions from the studies of the bond-orientational order parameters. Our results demonstrate that the orientational correlations, if measured by the heights of the peaks in the TCF, significantly increase on cooling. This rise in the orientational ordering is not captured properly by the Kirkwood’s superposition approximation. Detailed considerations of the peaks’ shapes in the TCF suggest the existence of a link between the orientational ordering and the slowdown of the system’s dynamics. Our findings support the view that the development of the orientational correlations in liquids may play a significant role in the liquids’ dynamics and that the considerations of the pair distribution function may not be sufficient to understand intuitively all the structural changes that happen with liquids on supercooling. In general, our results demonstrate that the considerations of the TCF are useful in the discussions of the liquid’s structures beyond the pair density function and interpreting the results obtained with the bond-orientational order parameters.

Concerning the formation of chains of particles in the Kob-Andersen (4:1) and Wahnstr{ö}m (1:1) model liquids on coolind and supercooling

“…[25]. Panels (a2), (b2), (c2) show the partial normalized structure functions SAA(q) obtained from the shown partial PDFs via the Fourier transform (5,6,7,9). In our calculations, Rmax ≈ 9.41, i.e., the half-length of the edge of the cubic simulation box.…”

“…In Fig. 4, we show the normalized partial pair density functions, g AA (r) (5), between the A particles and the corresponding normalized partial scattering intensities, S AA (q) (5,6,7,9), at selected temperatures. The results presented in these figures can be compared, for example, with the results shown in Fig.…”

“…There are multiple indications that the dynamic slowdown happening with supercooled liquids in the vicinity of the glass transition has a structural origin [1][2][3][4][5][6][7][8][9]. However, the nature of the structural features responsible for this slowdown is not well understood.…”

“…Earlier computer simulation studies were usually focused on considerations of local atomic environments of individual particles, essentially, limited by the nearest neighbor shells [1,2,[10][11][12]. In more recent studies, it has been realized that interactions with the second and more distant neighbors (mediumrange order) are also important for understanding the liquids' dynamics and, in particular, the relevant relaxation timescales [3,9,[12][13][14][15][16][17][18][19][20][21][22][23][24].…”

Comparing zero-parameter theories for the WCA and harmonic-repulsive melting lines

“…The above-mentioned approaches lead to zeroparameter predictions of the shape of the solid-fluid coexistence line for a given system. Here, we study the harmonic-repulsive [29][30][31][32][33][34][35][36] and the Weeks-Chandler-Andersen (WCA) [3,11,12,[37][38][39][40][41][42][43] pair potentials, both of which approach the hard-sphere potential at low temperatures. We can use any reference state point for the isomorph theory of melting [44].…”