5 research outputs found
Phase behaviour of coarse-grained fluids
Soft condensed matter structures often challenge us with complex many-body
phenomena governed by collective modes spanning wide spatial and temporal
domains. In order to successfully tackle such problems mesoscopic
coarse-grained (CG) statistical models are being developed, providing a
dramatic reduction in computational complexity. CG models provide an
intermediate step in the complex statistical framework of linking the
thermodynamics of condensed phases with the properties of their constituent
atoms and molecules. These allow us to offload part of the problem to the CG
model itself and reformulate the remainder in terms of reduced CG phase space.
However, such exchange of pawns to chess pieces, or ``Hamiltonian
renormalization'', is a radical step and the thermodynamics of the primary
atomic and CG models could be markedly different. Here, we present a
comprehensive study of the phase diagram including binodal and interfacial
properties of a novel soft CG model, which includes finite-range attraction and
supports liquid phases. Although the model is rooted in similar arguments to
the Lennard-Jones (LJ) atomic pair potential, its phase behaviour is
qualitatively different from that of LJ and features several anomalies such as
an unusually broad liquid range, change in concavity of the liquid coexistence
branch with variation of the model parameters, volume contraction on fusion,
temperature of maximum density in the liquid phase and negative thermal
expansion in the solid phase. These results provide new insight into the
connection between simple potential models and complex emergent condensed
matter phenomena.Comment: 10 pages, full pape
Equilibrium Simulation of the Slip Coefficient in Nanoscale Pores
Accurate prediction of interfacial slip in nanoscale channels is required by
many microfluidic applications. Existing hydrodynamic solutions based on
Maxwellian boundary conditions include an empirical parameter that depends on
material properties and pore dimensions. This paper presents a derivation of a
new expression for the slip coefficient that is not based on the assumptions
concerning the details of solid-fluid collisions and whose parameters are
obtainable from \textit{equilibrium} simulation. The results for the slip
coefficient and flow rates are in good agreement with non-equilibrium molecular
dynamics simulation.Comment: 11 pages, 4 figures, submitted to Phys Rev Let
Signature properties of water:Their molecular electronic origins
Water challenges our fundamental understanding of emergent materials properties from a molecular perspective. It exhibits a uniquely rich phenomenology including dramatic variations in behavior over the wide temperature range of the liquid into water’s crystalline phases and amorphous states. We show that many-body responses arising from water’s electronic structure are essential mechanisms harnessed by the molecule to encode for the distinguishing features of its condensed states. We treat the complete set of these many-body responses nonperturbatively within a coarse-grained electronic structure derived exclusively from single-molecule properties. Such a “strong coupling” approach generates interaction terms of all symmetries to all orders, thereby enabling unique transferability to diverse local environments such as those encountered along the coexistence curve. The symmetries of local motifs that can potentially emerge are not known a priori. Consequently, electronic responses unfiltered by artificial truncation are then required to embody the terms that tip the balance to the correct set of structures. Therefore, our fully responsive molecular model produces, a simple, accurate, and intuitive picture of water’s complexity and its molecular origin, predicting water’s signature physical properties from ice, through liquid–vapor coexistence, to the critical point