Atomistic Potentials for Trisiloxane, Alkyl Ethoxylate, and Perfluoroalkane-Based Surfactants with TIP4P/2005 and Application to Simulations at the Air–Water Interface

The mechanism of superspreading, the greatly enhanced spreading of water droplets facilitated by trisiloxane surfactants, is still under debate, largely because the role and behavior of the surfactants cannot be sufficiently resolved by experiments or continuum simulations. Previous molecular dynamics studies have been performed with simple model molecules or inaccurate models, strongly limiting their explanatory power. Here we present a force field dedicated to superspreading, extending existing quantum-chemistry-based models for the surfactant and the TIP4P/2005 water model (Abascal et al. J. Chem. Phys., 2005, 123, 234505). We apply the model to superspreading trisiloxane surfactants and nonsuperspreading alkyl ethoxylate and perfluoroalkane surfactants at various concentrations at the air–water interface. We show that the developed model accurately predicts surface tensions, which are typically assumed important for superspreading. Significant differences between superspreading and traditional surfactants are presented and their possible relation to superspreading discussed. Although the force field has been developed for superspreading problems, it should also perform well for other simulations involving polymers or copolymers with water

Definition and Computation of Intermolecular Contact in Liquids Using Additively Weighted Voronoi Tessellation

We present a definition of intermolecular surface contact by applying weighted Voronoi tessellations to configurations of various organic liquids and water obtained from molecular dynamics simulations. This definition of surface contact is used to link the COSMO-RS model and molecular dynamics simulations. We demonstrate that additively weighted tessellation is the superior tessellation type to define intermolecular surface contact. Furthermore, we fit a set of weights for the elements C, H, O, N, F, and S for this tessellation type to obtain optimal agreement between the models. We use these radii to successfully predict contact statistics for compounds that were excluded from the fit and mixtures. The observed agreement between contact statistics from COSMO-RS and molecular dynamics simulations confirms the capability of the presented method to describe intermolecular contact. Furthermore, we observe that increasing polarity of the surfaces of the examined molecules leads to weaker agreement in the contact statistics. This is especially pronounced for pure water

Reconsidering Dispersion Potentials: Reduced Cutoffs in Mesh-Based Ewald Solvers Can Be Faster Than Truncation

Long-range dispersion interactions have a critical influence on physical quantities in simulations of inhomogeneous systems. However, the perceived computational overhead of long-range solvers has until recently discouraged their implementation in molecular dynamics packages. Here, we demonstrate that reducing the cutoff radius for local interactions in the recently introduced particle–particle particle−mesh (PPPM) method for dispersion [Isele-Holder et al., <i>J. Chem. Phys.</i>, <b>2012</b>, <i>137</i>, 174107] can actually often be faster than truncating dispersion interactions. In addition, because all long-range dispersion interactions are incorporated, physical inaccuracies that arise from truncating the potential can be avoided. Simulations using PPPM or other mesh Ewald solvers for dispersion can provide results more accurately and more efficiently than simulations that truncate dispersion interactions. The use of mesh-based approaches for dispersion is now a viable alternative for all simulations containing dispersion interactions and not merely those where inhomogeneities were motivating factors for their use. We provide a set of parameters for the dispersion PPPM method using either <i>i</i><b>k</b> or analytic differentiation that we recommend for future use and demonstrate increased simulation efficiency by using the long-range dispersion solver in a series of performance tests on massively parallel computers

Reconsidering Dispersion Potentials: Reduced Cutoffs in Mesh-Based Ewald Solvers Can Be Faster Than Truncation

Long-range dispersion interactions have a critical influence on physical quantities in simulations of inhomogeneous systems. However, the perceived computational overhead of long-range solvers has until recently discouraged their implementation in molecular dynamics packages. Here, we demonstrate that reducing the cutoff radius for local interactions in the recently introduced particle–particle particle−mesh (PPPM) method for dispersion [Isele-Holder et al., <i>J. Chem. Phys.</i>, <b>2012</b>, <i>137</i>, 174107] can actually often be faster than truncating dispersion interactions. In addition, because all long-range dispersion interactions are incorporated, physical inaccuracies that arise from truncating the potential can be avoided. Simulations using PPPM or other mesh Ewald solvers for dispersion can provide results more accurately and more efficiently than simulations that truncate dispersion interactions. The use of mesh-based approaches for dispersion is now a viable alternative for all simulations containing dispersion interactions and not merely those where inhomogeneities were motivating factors for their use. We provide a set of parameters for the dispersion PPPM method using either <i>i</i><b>k</b> or analytic differentiation that we recommend for future use and demonstrate increased simulation efficiency by using the long-range dispersion solver in a series of performance tests on massively parallel computers

Reconsidering Dispersion Potentials: Reduced Cutoffs in Mesh-Based Ewald Solvers Can Be Faster Than Truncation

Long-range dispersion interactions have a critical influence on physical quantities in simulations of inhomogeneous systems. However, the perceived computational overhead of long-range solvers has until recently discouraged their implementation in molecular dynamics packages. Here, we demonstrate that reducing the cutoff radius for local interactions in the recently introduced particle–particle particle−mesh (PPPM) method for dispersion [Isele-Holder et al., <i>J. Chem. Phys.</i>, <b>2012</b>, <i>137</i>, 174107] can actually often be faster than truncating dispersion interactions. In addition, because all long-range dispersion interactions are incorporated, physical inaccuracies that arise from truncating the potential can be avoided. Simulations using PPPM or other mesh Ewald solvers for dispersion can provide results more accurately and more efficiently than simulations that truncate dispersion interactions. The use of mesh-based approaches for dispersion is now a viable alternative for all simulations containing dispersion interactions and not merely those where inhomogeneities were motivating factors for their use. We provide a set of parameters for the dispersion PPPM method using either <i>i</i><b>k</b> or analytic differentiation that we recommend for future use and demonstrate increased simulation efficiency by using the long-range dispersion solver in a series of performance tests on massively parallel computers