We obtain multiple solutions for the zero mass Schrödinger–Poisson–Slater equation \( - \Delta u + \left( \frac{1}{4 \pi | x |} *u^2 \right) u = \lambda g (x) | u |^{p - 2} u + | u |^{6 - 2} u \text {, }\qquad u \in \mathcal {D}^{1, 2} (\mathbb {R}^3) \) for \(\lambda \gg 1\) , where \(p \in (4, 6)\) and \(g \in L^{6 / (6 - p)} (\mathbb {R}^3)\) . The crucial \((\operatorname {PS})_c\) condition is verified using a simpler method. Similar multiplicity result is also obtained for related equation with an external potential.