LTspice diode model parallel capacitance
The capacitance of a diode is a function of the bias. The D model has zero-bias capacitance as a parameter. For example, the OnSemi 1N5819 model has Cjo of 110pF.
Edit:
Schottky junction capacitance is:
Cj = \$\frac{\text{Cjo}}{(1-\text {Vf}/ \text{Vj})^{M}}\$
For the 1N5819 mentioned above, Cjo = 110pF,  M = 0.35 and Vj = 1.0 (default).
Modelling the capacitance as a fixed parallel capacitor would be very inaccurate.
For very high frequencies, this is an interesting paper showing modeling of the package parasitics as well.