“…which has been studied by several researchers, see for example [1,2,5,12,14], [16] for a problem in a bounded domain. Usually, to obtain the existence and multiplicity of solutions, the authors require a restriction on the norm of the term h(x) and thus (1.2) is regarded as a perturbation of the equation −∆u + V (x)u = f (x, u), x ∈ R 2 .…”