“…On the other hand, the argument in [40,46, see Lemma 4.1] becomes invalid due to the lack of positive assumption onĜ(x, η) (i.e.,Ĝ(x, η) > 0). Motivated by the works [27,33,40,46], we further develop the approach in [29,34,35] to find ground state solution of Nehari-Pankov type for (1.1). Our approach is based on finding a proper subset E + 0 of E \ E -(see (3.4) for the definition) such that, for any η ∈ E + 0 , there exist t = t(η) > 0 and w = w(η) ∈ Esatisfying w + tη ∈ N -, then we can derive a minimizing sequence on the Nehari-Pankov manifold by using the diagonal method, see Lemma 3.9.…”