Abstract. We propose a phase field model that approximates its limiting sharp interface model (free boundary problem) up to second order in interface thickness. A broad range of double-well potentials can be utilized so long as the dynamical coefficient in the phase equation is adjusted appropriately. This model thereby assures that computation with particular value of interface thickness ε, will differ at most by O(ε 2 ) from the limiting sharp interface problem. As an illustration, the speed of a traveling wave of the phase field model is asymptotically expanded to demonstrate that it differs from the speed of the traveling wave of the limit problem by O(ε 2 ).
1.Introduction. Interface problems arising from solidification have been studied extensively in mathematics and physics for more than a century [29]. The mathematical study began with Lamè and Clapeyron [23] in 1831 who modeled the freezing of the ground using the heat equation, latent heat across the interface, and the condition that the temperature at the interface remains at the equilibrium freezing temperature. Reformulated in 1889, this problem became known as the classical Stefan model [31], and can be stated as follows. Determine the temperature, T (x, t), and the interface, Γ(t), satisfying the system of equations,