Resistor example 1D - Initial conditions explanation

This page explains the following code snipped from the 1D Resistor example:

Initial conditions

#Bias Voltage on the Contacts
contact name=VSS voltage supply=0.0
contact name=GND voltage supply=0.0

#Initial Guess at Zero Bias
sel z=(-$Vt*log(-($Doping+$small)/$ni)) name=DevPsi
sel z=$ni*exp(DevPsi/0.025) name=Elec
sel z=$ni*exp(-DevPsi/0.025) name=Hole

#DC Solve at Zero Bias
device