The relationship between the injected current density j₀ and the dominant fundamental oscillation frequency f of a virtual cathode in a one-dimensional grounded infinite planar drift space of length L is determined numerically. If the electrons, each of mass m_e and charge e, are injected with velocity v 0, it is found that for j₀ >> m _ev₀³/18πeL², f~ √j₀ which is in contrast to the relation f ~ √j₀ reported by earlier workers.