The conductance fluctuations for various types for two-- and three--dimensional disordered systems with hard wall and periodic boundary conditions are studied, all the way from the ballistic (metallic) regime to the localized regime. It is shown that the universal conductance fluctuations (UCF) depend on the boundary conditions. The same holds for the metal to insulator transition. The conditions for observing the UCF are also given.Comment: 4 pages RevTeX, 5 figures include

The probability distribution of the conductance p(g) of disordered 2d and 3d systems is calculated by transfer matrix techniques. As expected, p(g) is Gaussian for extended states while for localized states it is log-normal. We find that at the mobility edge p(g) is highly asymmetric and universal.Comment: 3 pages RevTeX, 6 figures included, submitted to Physica

Several phenomena related to the critical behavior of noninteracting electrons in a disordered twodimensional tight-binding system with a magnetic field are studied. Localization lengths, critical exponents, and density of states are computed using transfer-matrix techniques. Scaling functions of isotropic systems are recovered once the dimension of the system in each direction is chosen proportional to the localization length. It is also found that the critical point is independent of the propagation direction, and that the critical exponents for the localization length for both propagating directions are equal to that of the isotropic system, Ϸ 7 3 . We also calculate the critical value ⌳ c of the scaling function for both the isotropic and the anisotropic system. It is found that ⌳ c iso ϭͱ⌳ c x ⌳ c y . Detailed numerical studies of the density of states n(E) for the isotropic system reveal that for an appreciable amount of disorder, the critical energy is off the band center.