Hi, all I have an oscillator which oscillates at a certain frequency when I calculate the loaded resistance of the tank, the real value of the input impedance peak of the tank shifts from the expected frequency with the parasitic capacitance taken into consideration but it seems there are parasitic capacitances varying with the frequency that weren't taken into consideration how can I get these capacitances?

Show us your circuit, so we can help you. The varactor and transistor capacitances are extremely non-linear, for example. The inductor model itself can be very complex.