Detecting vapour bubbles in simulations of metastable water

Abstract

Thermodynamics and kinetics of bubble nucleation: Simulation methodology J. Chem. Phys. 137, 074109 (2012) The investigation of cavitation in metastable liquids with molecular simulations requires an appropriate definition of the volume of the vapour bubble forming within the metastable liquid phase. Commonly used approaches for bubble detection exhibit two significant flaws: first, when applied to water they often identify the voids within the hydrogen bond network as bubbles thus masking the signature of emerging bubbles and, second, they lack thermodynamic consistency. Here, we present two grid-based methods, the M-method and the V-method, to detect bubbles in metastable water specifically designed to address these shortcomings. The M-method incorporates information about neighbouring grid cells to distinguish between liquid-and vapour-like cells, which allows for a very sensitive detection of small bubbles and high spatial resolution of the detected bubbles. The V-method is calibrated such that its estimates for the bubble volume correspond to the average change in system volume and are thus thermodynamically consistent. Both methods are computationally inexpensive such that they can be used in molecular dynamics and Monte Carlo simulations of cavitation. We illustrate them by computing the free energy barrier and the size of the critical bubble for cavitation in water at negative pressure. © 2014 AIP Publishing LLC. [http://dx

Wetting and cavitation pathways on nanodecorated surfaces

“…34 The trend shows that the atomistic barrier is always less than the macroscopic one. These findings are in agreement with previous simulation studies 35,36 which predict that CNT overestimates the height of the barrier for the case of homogeneous nucleation. The pressure at which disappears is designated as spinodal pressure for the Cassie–vapor transition, P Cvsp; the atomistic value for P Cvsp is less than the macroscopic counterpart.…”

Pressure control in interfacial systems: Atomistic simulations of vapor nucleation

“…A hybrid restrained Monte Carlo (hRMC) scheme 17,18 is adopted in order to cope with the problem of rare events 19 typical of nucleation and in order to compute the related free energy profile; the volume of the largest bubble is used as the order parameter. 20 The good agreement between macro-and microscopic results suggests that the intuitive argument of domains at different pressures is, indeed, at the origin of the artifacts associated with global barostats. A solution to these artifacts consists in using a local barostat that imposes the (local) force balance between a piston and the contacting liquid.…”

“…17 and 18. In this method, the atoms are subject to the extended potential U(r) + U k (r). Here U(r) is the TFS-LJ interaction, U k (r) = k/2(V V (r) − V * V ) 2 is the biasing term where V V (r) is the current volume of the largest bubble in the system estimated with the M-method 20 and V * V is the target value of the bubble volume.…”

“…We compute the vapor nucleation free-energy barrier as a function of the largest vapor bubble in the system, V V , estimated using the M-method. 20 The method consists of several steps. (i) Particles are labeled as liquid-like if they have more than five particles closer than 1.6 σ, and vapor-like otherwise.…”

Effect of entropy on the nucleation of cavitation bubbles in water under tension

“…A committor analysis performed at ambient temperature and negative pressures suggests that the volume of the largest bubble constitutes a good reaction coordinate for cavitation [24]. Estimates for the volume v of every bubble present in the system are obtained by use of the V-method, [25] which is designed to give thermodynamically consistent bubble volumes, i.e., volumes consistent with the nucleation theorem. The V-method consists of two steps.…”