[en] A new class of particle simulation models has been developed which eliminates the high-frequency space charge oscillations while keeping the low-frequency ion-density fluctuations unmodified. Physically, the quasineutrality is maintained as the adiabatic electrons follow the ion-density fluctuations so as to Debye shield the resultant electrostatic potential. It is, therefore, possible to use the integration time step comparable to the characteristic time scale of the low-frequency oscillations so that realistic plasma parameters can be used in the present simulation model. Applications to the ion sound wave propagation, ion-ion two-stream instability, and the low-frequency fluctuation spectrum in a magnetic field are given. How to include the nonadiabatic electrons in the model is also discussed