Density correlation in liquid surfaces: Bedeaux-Weeks high order terms and non capillary wave background

Hernández‐Muñoz, Jose; Chacón, Enrique; Tarazona, P.

doi:10.1063/1.5049874

Cited by 5 publications

(4 citation statements)

References 41 publications

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“…Eq predicts a ∼ q –2 divergence for G ( z 1 , z 2 , q ) at low q . This has been shown to be a reasonable approximation for the typical sizes employed in the MD simulations of liquid surfaces . However, for the lipid membranes studied here and also for graphene sheets, the contributions from higher-order terms are very important.…”

Section: Computational and Theoretical Backgroundmentioning

confidence: 56%

“…This has been shown to be a reasonable approximation for the typical sizes employed in the MD simulations of liquid surfaces. 42 However, for the lipid membranes studied here and also for graphene sheets, 31 the contributions from higher-order terms are very important. Hence, to ensure convergence, we included up to n BW = 20 terms in the calculations of the BW series.…”

Section: Computational and Theoretical Backgroundmentioning

confidence: 84%

“…The BW series in eq gives the contribution of the mesoscopic surface fluctuations to the DCF. The MD result for G ( z 1 , z 2 , q ), in eq includes also contributions arising from fluctuations at molecular length-scales . We will refer to these contributions as the correlation background , G b = G – G BW , which includes contributions arising from peristaltic fluctuations of the membrane thickness and the 2D compressibility modes of the lipid bilayer.…”

Section: Computational and Theoretical Backgroundmentioning

confidence: 99%

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Bending Modulus of Lipid Membranes from Density Correlation Functions

Hernández‐Muñoz

Bresme

Tarazona

et al. 2022

J. Chem. Theory Comput.

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The bending modulus κ quantifies the elasticity of biological membranes in terms of the free energy cost of increasing the membrane corrugation. Molecular dynamics (MD) simulations provide a powerful approach to quantify κ by analyzing the thermal fluctuations of the lipid bilayer. However, existing methods require the identification and filtering of non-mesoscopic fluctuation modes. State of the art methods rely on identifying a smooth surface to describe the membrane shape. These methods introduce uncertainties in calculating κ since they rely on different criteria to select the relevant fluctuation modes. Here, we present a method to compute κ using molecular simulations. Our approach circumvents the need to define a mesoscopic surface or an orientation field for the lipid tails explicitly. The bending and tilt moduli can be extracted from the analysis of the density correlation function (DCF). The method introduced here builds on the Bedeaux and Weeks (BW) theory for the DCF of fluctuating interfaces and on the coupled undulatory (CU) mode introduced by us in previous work. We test the BW-DCF method by computing the elastic properties of lipid membranes with different system sizes (from 500 to 6000 lipid molecules) and using coarse-grained (for POPC and DPPC lipids) and fully atomistic models (for DPPC). Further, we quantify the impact of cholesterol on the bending modulus of DPPC bilayers. We compare our results with bending moduli obtained with X-ray diffraction data and different computer simulation methods.

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Section: Computational and Theoretical Backgroundmentioning

confidence: 56%

Section: Computational and Theoretical Backgroundmentioning

confidence: 84%

Section: Computational and Theoretical Backgroundmentioning

confidence: 99%

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Bending Modulus of Lipid Membranes from Density Correlation Functions

Hernández‐Muñoz

Bresme

Tarazona

et al. 2022

J. Chem. Theory Comput.

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“…This is explicit in derivations of interfacial Hamiltonians from more microscopic Landau-Ginzburg-Wilson (LGW) models in which they are identified via a constrained minimization, equivalent to a mean-field (MF) approximation of the trace over microscopic degrees of freedom. This means that binding potentials have been missing an entropic contribution arising from the multiplicity of microscopic configurations that correspond to a given interfacial one -a feature which is known to be important in molecular descriptions of free interfaces [26][27][28][29]. The entropic contribution to the binding potential is akin to a thermal Casimir effect -the force between two walls due to the restriction of bulk fluctuations in a confined fluid [30][31][32][33].…”

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confidence: 99%

Casimir contribution to the interfacial Hamiltonian for 3D wetting

Squarcini,

Romero-Enrique,

Parry

2022

Preprint

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Previous treatments of three-dimensional (3D) short-ranged wetting transitions have missed an entropic or low temperature Casimir contribution to the binding potential describing the interaction between the unbinding interface and wall. This we determine by exactly deriving the interfacial model for 3D wetting from a more microscopic Landau-Ginzburg-Wilson Hamiltonian. The Casimir term changes the interpretation of fluctuation effects occurring at wetting transitions so that, for example, mean-field predictions are no longer obtained when interfacial fluctuations are ignored. While the Casimir contribution does not alter the surface phase diagram, it significantly increases the adsorption near a first-order wetting transition and changes completely the predicted critical singularities of tricritical wetting, including the non-universality occurring in 3D arising from interfacial fluctuations. Using the numerical renormalization group we show that, for critical wetting, the asymptotic regime is extremely narrow with the growth of the parallel correlation length characterised by an effective exponent in quantitative agreement with Ising model simulations, resolving a longstanding controversy.

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Structure of liquid–vapor interfaces: Perspectives from liquid state theory, large-scale simulations, and potential grazing-incidence x-ray diffraction

Höfling,

Dietrich

2024

The Journal of Chemical Physics

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Grazing-incidence x-ray diffraction (GIXRD) is a scattering technique that allows one to characterize the structure of fluid interfaces down to the molecular scale, including the measurement of surface tension and interface roughness. However, the corresponding standard data analysis at nonzero wave numbers has been criticized as to be inconclusive because the scattering intensity is polluted by the unavoidable scattering from the bulk. Here, we overcome this ambiguity by proposing a physically consistent model of the bulk contribution based on a minimal set of assumptions of experimental relevance. To this end, we derive an explicit integral expression for the background scattering, which can be determined numerically from the static structure factors of the coexisting bulk phases as independent input. Concerning the interpretation of GIXRD data inferred from computer simulations, we extend the model to account also for the finite sizes of the bulk phases, which are unavoidable in simulations. The corresponding leading-order correction beyond the dominant contribution to the scattered intensity is revealed by asymptotic analysis, which is characterized by the competition between the linear system size and the x-ray penetration depth in the case of simulations. Specifically, we have calculated the expected GIXRD intensity for scattering at the planar liquid–vapor interface of Lennard-Jones fluids with truncated pair interactions via extensive, high-precision computer simulations. The reported data cover interfacial and bulk properties of fluid states along the whole liquid–vapor coexistence line. A sensitivity analysis shows that our findings are robust with respect to the detailed definition of the mean interface position. We conclude that previous claims of an enhanced surface tension at mesoscopic scales are amenable to unambiguous tests via scattering experiments.

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Density correlation in liquid surfaces: Bedeaux-Weeks high order terms and non capillary wave background

Cited by 5 publications

References 41 publications

Bending Modulus of Lipid Membranes from Density Correlation Functions

Bending Modulus of Lipid Membranes from Density Correlation Functions

Casimir contribution to the interfacial Hamiltonian for 3D wetting

Structure of liquid–vapor interfaces: Perspectives from liquid state theory, large-scale simulations, and potential grazing-incidence x-ray diffraction

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