$useconstId

Since DDCC solver is solved by input bias, therefore it is hard to obtain the exactly desired current density. $useconstId is a command for the program to get a certain Id value by tuning the bias itself to reach the required gate current. However, it is very time consuming.

$useconstId
Id_value V_trial_min V_trial_max Vd_step_min Precision

The Ig_value is the current density of gate ( or Base). The unit is A/cm since it is 2D simulation.  The Id is define as (Jpd-Jnd). Be careful about the sign.

The simulation program need to set Vd = constant and Vd (VC) in a range. Vs (VE) can be treated as emitter. 
The program will try in a Vd bias ranging from $Vd+V_{trial,min}<Vg< Vg+V_{trial,max}$ in a minimum Vd interval Vd_step_min.
Once the current error is within   Precision

For example 
$Schottky     
1.4
$gatebias     
0.9   0.9   0.01   
$drainbias     
0.5   5.0   0.5   
$sourcebias     
0.0
$useconstId
1.0e-3 -0.2 0.2 1.0e-4 1.0e-3

The $useconstId setting in GUI interface is here
After setting up the general structure, press Material Parameter and fill in these fields!