Junction Potential parameter in Keysight Genesys
The VJ parameter is used by many SPICE-derived simulators for their diode models. It doesn't affect the I-V characteristics of the diode, but rather the capacitance characteristic.

The junction capacitance characteristic is given by

$$C_j(V)=\frac{C_j(0)}{\sqrt{1-V/V_j}}.$$

(source)

The total capacitance of the diode is 

$$C=C_j+C_d$$

with \$C_j\$ being dominant when the diode is reverse biased, and the diffusion capacitance \$C_d\$ being dominant when the diode is forward biased.

If you want to set the forward voltage of the diode, you need to look at the Shockley diode equation

$$I(V) = I_s \exp\left(\frac{V}{nV_T}-1\right)$$ 

and set the corresponding SPICE parameters IS and N (and possibly the series resistance RS) to achieve the forward voltage (and reverse leakage) to match your physical diode.