  The existing discrete variational derivative method is only second-order
accurate and fully implicit. In this paper, we propose a framework to construct
an arbitrary high-order implicit (original) energy stable scheme and a
second-order semi-implicit (modified) energy stable scheme. Combined with the
Runge--Kutta process, we can build an arbitrary high-order and unconditionally
(original) energy stable scheme based on the discrete variational derivative
method. The new energy stable scheme is implicit and leads to a large sparse
nonlinear algebraic system at each time step, which can be efficiently solved
by using an inexact Newton type algorithm. To avoid solving nonlinear algebraic
systems, we then present a relaxed discrete variational derivative method,
which can construct second-order, linear, and unconditionally (modified) energy
stable schemes. Several numerical simulations are performed to investigate the
efficiency, stability, and accuracy of the newly proposed schemes.
