“…The highest order term models a small amount of surface diffusion, which smooths out the facets somewhat. In the square Swift-Hohenberg (SH) equation ∂ t u = −(1 + ∆) 2 u − βu + ηu 3 − u 5 + α |∇u| 2 ∇u , α > 0, β, η ∈ R, studied in [12,22,20,30], and the square phase field crystal (SPFC) equation ∂ t u = ∆ γ 0 u + γ 1 ∆u + ε 2 ∆ 2 u − ∇ · |∇u| 2 ∇u , γ 0 ∈ R, γ 1 > 0, studied in [16,19,20,30], the 4-Laplacian term gives preference to square-symmetry patterns. In general, such localized structures play important roles in biological, chemical, and physical processes [23].…”