Molecular dynamics simulations for LJ particles and LJ and HP chains

These simulations were carried out using the HOOMD-blue package (version 2.5.0) on GPUs (Glaser et al., 2015). All the particles or beads have the same diameter σ , which sets the unit of lengths, and the same mass m . The units for number density, temperature, interfacial tension, and time are σ−3 , ε/kB , ε/σ2 , and mσ2/ε≡τ , respectively. Below we will often leave out these units in order to reduce clutter. The MD simulations were carried out at constant particle (or bead) number (N), volume, and temperature. Temperature was regulated by the Langevin thermostat with a friction coefficient of 0.1 m/τ . The time step was 0.005 τ for particle systems and 0.001 τ for chain systems. For identifying the dense-phase morphologies of a given system, the initial densities were scanned over a range as described above. The presentation below applies to simulations where a slab morphology was formed and used to calculate binodals and interfacial tension.

The initial densities were 0.3 for LJ particles and 0.25 for LJ and HP chains. Separate simulations were carried out over a range of temperatures. To investigate the effects of system size and L _z /L _x ratio, we chose N in the range of 1,000–10,000, and L _z /L _x from 1.25 to 33.3 for LJ particles, from 1.16 to 18.2 for LJ chains, and 1.5 to 5 for HP chains. For LJ particles, the simulation length was 10 million steps, but was extended to 100 or 200 million steps when multiple slabs took a long time to fuse into a single slab (at N ≥ 6,000 and L _z /L _x ≥ 20). The same was true for LJ chains, except that the longer simulations were 100–300 million steps and applied to more cases (N as low as 4,000 and L _z /L _x as low as 2). The simulation length was 100 million steps for HP chains. The time interval for saving snapshots was 1,000 time steps for simulations with a total length of 10 million steps and 10,000 time steps for longer simulations.