Under the condition of n (u n ) = n |u n | 2 u n , by applying the linking theorem, Pankov obtained the existence of gap solitons. Pankov's result was then generalized to various type of nonlinear function f n , but most of studying works were concentrated on the case of n (t) = O (|t| s 1 ) as t → 0(s 1 ⩾ 1). In this paper, by ingeniously using Ekeland variational principle, for the nonlinearity which meets n (t) = O(|t| s 1 ) as t → 0 (s 1 ∈ (0, 1)), we obtain the existence of gap solitons, which supplements the existing ones and gives a positive answer in part to the open problem proposed by Pankov. KEYWORDS discrete nonlinear Schrödinger equations, Ekeland variational principle, gap solitons, periodic approximation Lu n − u n = n (u n ) , n ∈ Z,where {u n } n∈Z is a real valued sequence, = ±1, is the temporal frequency, f n (t) is continuous in t, f n + T (t) = f n (t) for each n ∈ Z, and f n is supposed to be gauge invariant, ie, n (e i t) = e i n (t), ∈ R, L is a Jacobi operator 9 given by Lu n = a n u n+1 + a n−1 u n−1 + b n u n , where {a n } , {b n } are real valued T-periodic sequences.Since L is a bounded and self-adjoint operator, the spectrum (L) of L has a band structure, ie, (L) is a union of a finite number of closed intervals. 9 Thus, the complement R ⧵ (L) consists of a finite number of open intervals called spectral Math Meth Appl Sci. 2018;41:6673-6682.wileyonlinelibrary.com/journal/mma