Water-like Anomalies and Phase Behavior of a Pair Potential that Stabilizes Diamond

Abstract

Water, silicon, silica, and other liquids that favor tetrahedral order display thermodynamic, dynamic, and structural anomalies in the pressure range in which they form tetrahedrally coordinated crystals. The tetrahedral order in these liquids is induced by anisotropic hydrogen bonding or covalent interactions, or, in ionic melts, by an appropriate size ratio of the ions. Simple isotropic two-length scale models have been extensively used to understand the origin of anomalies in complex liquids. However, single-component isotropic liquids characterized to date generally do not stabilize tetrahedral crystals, and in the few cases that they do, it was found that the liquids do not display anomalies in the region of the tetrahedral crystal. This poses the question of whether it is possible for isotropic pair potentials to display water-like phase behavior and anomalies. In this work, we use molecular dynamics simulations to investigate the phase behavior and the existence and loci of anomalies of a single-component purely repulsive isotropic pair potential that stabilizes diamond in the ground state over a wide range of pressures. We demonstrate that, akin to water, silica, and silicon, the isotropic potential of Marcotte, Stillinger, and Torquato (MST) presents structural, dynamic, and thermodynamic anomalies in the region of stability of the tetrahedral crystal. The regions of anomalies of MST are nested in the T-p plane following the same hierarchy as in silica: the region of diffusional anomalies encloses the region of structural anomalies, which in turn contains the region of thermodynamic anomalies. To our knowledge, MST is the first example of pair potential for which water-like anomalies are associated with the formation of tetrahedral order.

Stability and Metastability of Liquid Water in a Machine-Learned Coarse-Grained Model with Short-Range Interactions

“…It has been previously shown that the sign of the slope of the crystallization line T h (p) follows that of the melting line T m (p) for the mW and mTIP4P/2005 REM monatomic SW water models, 56 as well as the all-atom TIP4P/2005, 100 TIP4P, 51 and TIP4P/Ice, 101 and other liquids with water-like anomalies. 102 The same is observed for ML-BOP, for which dT h /dp = 0 at p ≈ −150 MPa (Figure 4). The closeness in reentrant pressures for T h (p) and T m (p) seems to be a common characteristic of all water-like liquids.…”

Targeted Discovery of Low-Coordinated Crystal Structures via Tunable Particle Interactions

“…hR 3-α is one of the lowest-coordinated structures found in this study and is a 2-coordinated columnar structure where particles are hexagonally arranged and have nearest neighbors only within these columns, arranged along the c -axis. This structure seems to correspond to another structure found in a previous computational study investigating the pressure-induced structures of a diamond-type phase . Here, we find that the structure can be simulated without applying an elevated pressure.…”

Anomalous Diffusion: A Basic Mechanism for the Evolution of Inhomogeneous Systems

“…The recent interest in the study of complex systems has led to an increased focus on anomalous diffusion [4-7, 36, 42, 45], which has been described in biological systems [42][43][44], protostellar birth [47], complex fluids [48][49][50][51][52][53], electronic transportation [54][55][56][57][58][59], porous media and infiltration [60][61][62], drug delivery [63][64][65][66], fractal structures and networks [67][68][69][70][71], and in water's anomalous behavior [72][73][74], phase transitions in synchronizing oscillators [39,40,[75][76][77], to name a few.…”