  We propose a high-speed and accurate hybrid dynamic density functional theory
for the computer simulations of the phase separation processes of polymer melts
and blends. The proposed theory is a combination of the dynamic self-consistent
field (SCF) theory and a time-dependent Ginzburg-Landau type theory with the
random phase approximation (GRPA). The SCF theory is known to be accurate in
evaluating the free energy of the polymer systems in both weak and strong
segregation regions although it has a disadvantage of the requirement of a
considerable amount of computational cost. On the other hand, the GRPA theory
has an advantage of much smaller amount of required computational cost than the
SCF theory while its applicability is limited to the weak segregation region.
To make the accuracy of the SCF theory and the high-performance of the GRPA
theory compatible, we adjust the chemical potential of the GRPA theory by using
the SCF theory every constant time steps in the dynamic simulations. The
performance of the GRPA and the hybrid theories is tested by using several
systems composed of an A/B homopolymer, an AB diblock copolymer, or an ABC
triblock copolymer. Using the hybrid theory, we succeeded in reproducing the
metastable complex phase-separated domain structures of an ABC triblock
copolymer observed by experiments.
