We present results from detailed, atomistic molecular dynamics (MD) simulations of pure, strictly monodisperse linear and ring poly(ethylene oxide) (PEO) melts under equilibrium and nonequilibrium (shear flow) conditions. The systems examined span the regime of molecular weights (M w ) from sub-Rouse (M w < M e ) to reptation (M w ∼ 10 M e ), where M e denotes the characteristic entanglement molecular weight of linear PEO. For both PEO architectures (ring and linear), the predicted chain center-of-mass self-diffusion coefficients D G as a function of PEO M w are in remarkable agreement with experimental data. From the flow simulations under shear, we have extracted and analyzed the zero-shear viscosity of ring and linear PEO melts as a function of M w .

Results are presented for the density, free volume, self‐diffusion, structure, and conformation of short linear and cyclic n‐alkanes in their own melt and in blends at equal carbon number from detailed atomistic molecular dynamics (MD) simulations in the isothermal‐isobaric (NPT) statistical ensemble using the explicit‐atom optimized potentials for liquid simulations (OPLS‐AA) force‐field. In agreement with experimental data reported in an earlier study by von Meerwall et al. (2003), cyclic alkanes are characterized by higher densities and diffuse more slowly than their equivalent linear alkanes. Their configurations are also dominated by certain conformers whose exact shape depends on the molecular length n of the cyclic alkane. The smaller the value of n the more symmetric the shape of these conformers. The MD results support the findings of von Meerwall et al. (2003) that the overall (single average) diffusion coefficient of linear and cyclic alkanes in their blend is equal to the weight‐average of the diffusion coefficients of the neat species at the same temperature. Simulation results are also presented for the average size, individual diffusivities, and intermolecular CC pair distribution function of the two components (linear and cyclic) as a function of molecular weight and blend concentration in cyclic molecules.

Detailed molecular dynamics (MD) simulations of aqueous solutions of short DNA minicircles ranging in size from 30 to 180 bp were performed for the investigation of the structure and dynamics at an atomistic level, by employing the recently developed parmbsc1 force field. The resulting MD trajectories were analyzed for the determination of local conformation in terms of backbone torsion angles and interbase pair helical parameters, and very good agreement was observed with respect to relevant experimental data. Minor groove hydration exhibits a bimodal structure for all nucleobases, with water molecules residing in the first subshell of hydration forming a highly ordered, chiral water layer that conforms to the topological state of DNA, even adopting a twisted, figure-eight shape in the case of 180 bp minicircles. The mean-squared radius of gyration of the simulated DNA minicircles was found to scale with the number of base pairs, N bp, as ⟨R g 2⟩ ∼ N bp 2ν with ν ≈ 0.83, a scaling exponent in-between the values corresponding to a rigid rodlike behavior and the 3D self-avoiding walk limit for flexible chains. Ultrashort and very stiff 30 bp minicircles exhibit an unexpectedly pronounced degree of anisotropic diffusion, a phenomenon that is attenuated as the molecular length increases due to the emergence of out-of-plane bending motions.