We consider the following singularly perturbed semilinear elliptic problem: ε 2 Δu−u+u p=0 in Ω, u>0 in Ω and ∂u ∂ν =0 on ∂Ω, where Ω is a bounded smooth domain in R N , ε>0 is a small constant and p is a subcritical exponent. Let J ε[u]:=∫ Ω( ε 2 2 |∇u| 2+ 1 2 u 2− 1 p+1 u p+1) dx be its energy functional, where u∈H 1(Ω) . Ni and Takagi proved that for a single boundary spike solution u ε , the following asymptotic expansion holds J ε[u ε]=ε N 1 2 I[w]−c 1εH(P ε)+ o(ε) , where c 1>0 is a generic constant, P ε is the unique local maximum point of u ε and H( P ε ) is the boundary mean curvature function. In this Note, we obtain the following higher order expansion of J ε [ u ε ]: J ε[u ε]=ε N 1 2 I[w]−c 1εH(P ε)+ε 2[c 2(H(P ε)) 2+c 3R(P ε)]+ o(ε 2) , where c 2, c 3 are generic constants and R( P ε ) is the Ricci scalar curvature at P ε . In particular c 3>0. Applications of this expansion will be given. To cite this article: J. Wei, M. Winter, C. R. Acad. Sci. Paris, Ser. I 337 (2003).
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