Phase diagram for diblock copolymer melts from Langevin field-theoretic simulations

Field-theoretic simulations (FTS) provide fluctuation corrections to self-consistent field theory (SCFT) by simulating its field-theoretic Hamiltonian rather than applying the saddle-point approximation. Here, we apply Langevin FTS (L-FTS) to AB diblock copolymer melts, where the composition field fluctuates via Langevin dynamics but the saddle-point approximation is still applied to the pressure field that enforces incompressibility. The method is demonstrated to be one or two orders of magnitude faster than previous Monte Carlo simulations (MC-FTS), permitting the rapid formation of spontaneously ordered configurations and the accurate determination of their order-disorder transitions. The results are used to construct a phase diagram for diblock copolymer melts of high invariant polymerization index, N = 10⁴.