Nuclear quantum effects on the dynamics and glass behavior of a monatomic liquid with two liquid states

Abstract

We perform path integral molecular dynamics (PIMD) simulations of a monatomic liquid that exhibits a liquid-liquid phase transition (LLPT) and liquid-liquid critical point. PIMD simulations are performed using different values of the Planck's constant h, allowing us to study the behavior of the liquid as nuclear quantum effects (NQE, i.e., atoms delocalization) are introduced, from the classical liquid ( h=0) to increasingly quantum liquids ( h>0). By combining the PIMD simulations with the ring-polymer molecular dynamics (RPMD) method, we also explore the dynamics of the classical and quantum liquids. We find that (i) the glass transition temperature of the low-density liquid (LDL) is anomalous, i.e., TgLDL(P) decreases upon compression. Instead, (ii) the glass transition temperature of the high-density liquid (HDL) is normal, i.e., TgHDL(P) increases upon compression. (iii) NQE shift both TgLDL(P) and TgHDL(P) towards lower temperatures but NQE are more pronounced on HDL. We also study the glass behavior of the ring-polymer systems associated to the quantum liquids studied (via the PI formulation of statistical mechanics). There are two glass states in all the systems studied, LDA and HDA, which are the glass counterpart of LDL and HDL. In all cases, the pressure-induced LDA-HDA transformation is sharp, reminiscent of a first-order phase transition. In the low-quantum regime, the LDA-HDA transformation is reversible, with identical LDA forms before the compression and after the decompression. However, in the high-quantum regime, the atoms become more delocalized in the final LDA than in the initial LDA, raising questions on the reversibility of the LDA-HDA transformation.

The Importance of Nuclear Quantum Effects on the Thermodynamic and Structural Properties of Low-Density Amorphous Ice: A Comparison with Hexagonal Ice

“…63 The R g of the O and H atoms of water in ice I h and during the cooling-induced liquid-to-LDA transformation (P = 0.1 MPa) are shown in Figure 6b. Consistent with previous computational studies performed on water-like models, 32 R g (T) increases as the temperature is decreased (i.e., the O and H atoms become increasingly delocalized upon cooling at lower temperatures). The delocalization of the H atoms in ice I h and LDA is considerable.…”

“…For example, NQE are responsible for the difference in the melting temperature of H 2 O and D 2 O (δ T ≈ 4 K) as well as in the corresponding temperature of maximum density (δ T ≈ 7 K) and the glass transition temperature (δ T ≈ 10 K) . In addition, computer simulations of water-like models, show that the inclusion of NQE can have a significant impact on the thermodynamic, dynamical, and structural properties of the low-temperature liquid as well as the glass state. − At present, the role of NQE on LDA and HDA remains poorly understood.…”

The Harmonic and Gaussian Approximations in the Potential Energy Landscape Formalism for Quantum Liquids

“…In order to understand the role of quantum mechanics in the PEL formalism, we follow refs and − and perform PIMC simulations of the FJ liquid using different values of the Planck’s constant h . This allows us to simulate the same liquid in the classical limit ( h = 0) as well as in the quantum regime ( h > 0).…”