We propose a theoretical scheme for a hybrid simulation technique where self-consistent field theory and molecular dynamics simulation are combined (MD-SCF). We describe the detail of the main implementation issues on the evaluation of a smooth three-dimensional spatial density distribution and its special gradient based on the positions of particles. The treatments of our multiscale model system on an atomic scale or on a specific coarse-grained scale are carefully discussed. We perform a series of test simulations on this hybrid model system and compare the structural correlations on the atomic scale with those of classical MD simulations. The results are very encouraging and open a way to an efficient strategy that possess the main advantages common to the SCF and the atomistic approaches, while avoiding the disadvantages of each of the treatments.

In the framework of a recently developed scheme for a hybrid particle-field simulation technique where self-consistent field theory (SCF) and molecular dynamics (MD) are combined [ J. Chem. Phys. 2009 , 130 , 214106 ], specific coarse-grained models for phospholipids and water have been developed. We optimized the model parameters, which are necessary in evaluating the interactions between the particles and the density fields, so that the coarse-grained model can reproduce the structural properties of the reference particle-particle simulations. The development of these specific coarse-grained models suitable for hybrid particle-field simulations opens the way toward simulations of large-scale systems employing models with chemical specificity, especially for biological systems.

The parallel implementation of a recently developed hybrid scheme for molecular dynamics (MD) simulations (Milano and Kawakatsu, J Chem Phys 2009, 130, 214106) where selfconsistent field theory (SCF) and particle models are combined is described. Because of the peculiar formulation of the hybrid method, considering single particles interacting with density fields, the most computationally expensive part of the hybrid particle-field MD simulation can be efficiently parallelized using a straightforward particle decomposition algorithm. Benchmarks of simulations, including comparisons of serial MD and MD-SCF program profiles, serial MD-SCF and parallel MD-SCF program profiles, and parallel benchmarks compared with efficient MD program GROMACS 4.5.4 are tested and reported. The results of benchmarks indicate that the proposed parallelization scheme is very efficient and opens the way to molecular simulations of large scale systems with reasonable computational costs.

No abstract

We show that a strong segregation of a two-component surfactant system coupled to the local membrane curvature has a pronounced effect on the shape of unilamellae or closed vesicles. For an average flat lamella, the preferred periodicity in the local composition as well as the lamellar shape is calculated and depends on the ratio between surface tension and bending modulus. In the case of a closed visicle with a futed total area, there is no selected periodicity in contrast to the unilamellar case. For vesicles subjected to positive or negative inner pressure, we calculate their shape numerically, whereas when there is no added inner pressure, the shape is found analytically to be composed of circular sections.