  This letter revisits the energy quadratization (EQ) method by introducing a
novel and essential relaxation technique to improve its accuracy and stability.
The EQ method has witnessed significant popularity in the past few years.
Though acknowledging its effectiveness in designing energy-stable schemes for
thermodynamically consistent models, the primary known drawback is apparent,
i.e., its preserves a "modified" energy law represented by auxiliary variables
instead of the original variables. Truncation errors are introduced during
numerical calculations so that the numerical solutions of the auxiliary
variables are no longer equivalent to their original continuous definitions.
Even though the "modified" energy dissipation law is preserved, the original
energy dissipation law is not guaranteed. In this paper, we overcome this issue
by introducing a relaxation technique. The computational cost of this extra
technique is negligible compared with the baseline EQ method. Meanwhile, the
relaxed-EQ method holds all the baseline EQ method's good properties, such as
linearity and unconditionally energy stability. Then we apply the relaxed-EQ
method to several widely-used phase field models to highlight its
effectiveness.
