Bibliography - Pablo Debenedetti

1. Liu, Yang, Athanassios Z. Panagiotopoulos, and Pablo Debenedetti, 2011: Monte Carlo Simulations of High-Pressure Phase Equilibria of CO₂-H₂O Mixtures. Journal of Physical Chemistry, American Chemical Society, B(115 (20)), doi:10.1021/jp201520u 6629-6635
   [ Abstract ]

   Histogram-reweighting grand canonical Monte Carlo simulations were used to obtain the phase behavior of CO₂—H₂O mixtures over a broad temperature and pressure range (50 °C ≤ T ≤ 350 °C, 0 ≤ P ≤ 1000 bar). We performed a comprehensive test of several existing water (SPC, TIP4P, TIP4P2005, and exponential-6) and carbon dioxide (EPM2, TraPPE, and exponential-6) models using conventional Lorentz—Berthelot combining rules for the unlike-pair parameters. None of the models we studied reproduce adequately experimental data over the entire temperature and pressure range, but critical assessments were made on the range of T and P where particular model pairs perform better. Away from the critical region (T ≤ 250 °C), the exponential-6 model combination yields the best predictions for the CO₂-rich phase, whereas the TraPPE/TIP4P2005 model combination provides the most accurate coexistence composition and pressure for the H₂O-rich phase. Near the critical region (250 °C ≤ T ≤ 350 °C), the critical points are not accurately estimated by any of the models studied, but the exponential-6 models are able to qualitatively capture the critical loci and the shape of the phase envelopes. Local improvements can be achieved at specific temperatures by introducing modification factors to the Lorentz—Berthelot combining rules, but the modified combining rule is still not able to achieve global improvements over the entire temperature and pressure range. Our work points to the challenge and importance of improving current atomistic models so as to accurately predict the phase behavior of this important binary mixture.

2. Sarupria, S., and Pablo Debenedetti, 2011: Molecular Dynamics Study of Carbon Dioxide Hydrate Dissociation. Journal of Physical Chemistry, American Chemical Society, A(115 (23)), doi:10.1021/jp110868t 6102-6111
   [ Abstract ]

   We present results from a molecular dynamics study of the dissociation behavior of carbon dioxide (CO₂) hydrates. We explore the effects of hydrate occupancy and temperature on the rate of hydrate dissociation. We quantify the rate of dissociation by tracking CO₂ release into the liquid water phase as well as the velocity of the hydrate
   liquid water interface. Our results show that the rate of dissociation is dependent on the fractional occupancy of each cage type and cannot be described simply in terms of overall hydrate occupancy. Specifically, we find that hydrates with similar overall occupancy differ in their dissociation behavior depending on whether the small or large cages are empty. In addition, individual cages behave differently depending on their surrounding environment. For the same overall occupancy, filled small and large cages dissociate faster in the presence of empty large cages than when empty small cages are present. Therefore, hydrate dissociation is a collective phenomenon that cannot be described by focusing solely on individual cage behavior.

3. Liu, Yang, Athanassios Z. Panagiotopoulos, and Pablo Debenedetti, 2010: Finite-size scaling study of the vapor-liquid critical properties of confined fluids: crossover from three dimensions to two dimensions. Journal of Chemical Physics, 132, doi:10.1063/1.3377089 144107-144107-10
   [ Abstract ]

   We perform histogram-reweighting grand canonical Monte Carlo simulations of the Lennard-Jones fluid confined between two parallel hard walls and determine the vapor-liquid critical and coexistence properties in the range of
   σ≤H≤6σ
   and 10σ≤L_x ,L_y
   ≤28σ, where H is the wall separation, L_x=L_y is the system size and
   is the characteristic length. By matching the probability distribution of the ordering operator, P(M), to the three-dimensional 3(D) and two-dimensional 2(D) Ising universality classes according to the mixed-field finite-size scaling approach, we establish a “phase diagram” in the (H,L) plane, showing the boundary between four types of behavior: 3D, quasi-3D, quasi-2D, and 2D. In order to facilitate 2D critical point calculation, we present a four-parameter analytical expression for the 2D Ising universal distribution. We show that the infinite-system-size critical points obtained by extrapolation from the apparent 3D and 2D critical points have only minor differences with each other. In agreement with recent reports in the literature [Jana et al., J. Chem. Phys. 130, 214707
   2009], we find departure from linearity in the relationship between critical temperature and inverse wall separation, as well as nonmonotonic dependence of the critical density and the liquid density at coexistence upon wall separation. Additional studies of the ST2 model of water show similar behavior, which suggests that these are quite general properties of confined fluids. © 2010 American Institute of Physics.

4. Debenedetti, Pablo, and S. Sarupria, 2009: Hydrate Molecular Ballet. Science, 326(5956), doi:10.1126/science.1183027 1070-1071
   [ Abstract ]

   Hydrates are crystalline solids in which guest molecules are trapped within polyhedral water cages (1). They are important in hydrocarbon processing (2) and could play a major role in sustainable energy production (3, 4). Methane hydrate occurs naturally and in vast quantities on ocean floors and in permafrost, with implications for climate change and energy recovery (2). However, the molecular mechanisms leading to hydrate formation are poorly understood; this knowledge gap affects not just the science and technology of these materials, but our comprehension of hydrophobicity (5) and of disorder-order phase transitions. On page 1095 of this issue, Walsh et al. report a computational tour de force that offers a fascinating glimpse of the molecular events leading to methane hydrate formation (6).

Direct link to page: http://cmi.princeton.edu/bibliography/results.php?author=3469