ZHANG, Zhitao, YU, Meng and ZHENG, Xiaotian. Existence of nontrivial solutions to Schrödinger systems with linear and nonlinear couplings via Morse theory. Topological Methods in Nonlinear Analysis. Online. 23 June 2023. Vol. 61, no. 2, pp. 701 - 716. [Accessed 21 December 2025]. DOI 10.12775/TMNA.2022.032.