“…For the existence and qualitative properties of solutions for the nonlinear Choquard equation (1.1), we refer the reader to [2,3,5,9,10,14,17,26,27,31,32,34,35] and references therein. In particular, for p > 2, the existence of nodal solutions for the Choquard equation is an appealing aspect which is investigated in [5,8,11,13,15,16,23] by the variational method. In the physical case, for p = 2, the existence of nodal solutions for (1.1) only has few results.…”