OK. Thank for your comment. You are completely right.
My question was:
Is there any simple way to get approximately close result in hand calculation to the result from simulation in Cadenec or Hspice?!
This means that result of hand calculation and simulation is not the same. And it is asking about hand calculation since the reason why these two are not the same comes back to hand calculation.
Anyway, I have just recently found that one way is entering one more parameter like η in the DC current formula. In this way, the new formula could be like:
I = 0.5 µ cox (W/L) (Vgs-Vth)^2 * [1/η]
In other words, with comparing result of hand calculation and simulation result, we can find the value of η.
But, as you know, it is still prone to error.
I am wondering if anybody discover other better ways!
Anyhow, I thank you for your nice and good points.
Good Luck,