ideal bjt pspice
Viren,
What are you trying to fit? Your original message has output characteristics curve, but now you are trying to play with parameters for a Gummel curve. NE is just a fitting parameter for Ib at low Vbe to model the increase in base current. It will usually be anywhere between 1.0 (ideal) to 2.0. ISE is the current when Vbe=0 or where Ib intercepts the y-axis when extropolated.
I have attached a document "Gummel-Poon Bipolar Model : Model Description & Parameter Extraction." I downloaded this from the web a long time ago (but I don't remember where), so someone maybe able to find it and provide the link, if they don't want to use any points.
Page 5 has the equations for IB related to ISE and NE.
As Flatulent had said before, modelling a transistor is a "craft" which requires understanding of the measurement and extraction methodology, plus understanding of the device physics of a bjt.
On page 13 of this document, has a recommended procedure to extract bipolar G-P parameters. There are a lot of figures showing how each parameter is measured, which is helpful.