[en] The one-component plasma (OCP), an electron gas on a positive background, and the subsystem of free charges in a two-component plasma (TCP) is investigated using a quasi-classical approach. Quantum effects such as the Heisenberg uncertainty principle and the Pauli exclusion principle are incorporated into our model by effective potentials. In case of the OCP the symmetry effects are of special interest whereas in case of TCP the Heisenberg effects play the significant role. The method of Slater sums is used to obtain effective potentials. Monte Carlo simulations for both OCP and TCP were carried out to calculate the Coulombic energy, the effective energy, and the pair-distribution functions. (orig.)