This page is an attempt to summarize known differences between modeling syntax in LTspice and SPICE3. If you know of any that should be included, please let me know.
nonlinear dependent sources
From the LTspice help files, in modeling nonlinear dependent sources (i.e., arbitrary behavioral voltage or current sources),
LTspice uses the caret character, ^, for Boolean XOR and “**” for exponentiation. … This means that when you import a 3rd party model that was targeted at a 3rd party simulator, you may need to translate the syntax such as x^y to x**y or even pwr(x,y).
resistors
From Helmut Sennewald:
I have seen a very few models using the syntax of Spice3
for resistor models. … The name of the resistor model is exchanged with the value.Spice3:
RFDBCK 3 33 10K RMOD
PPSICE, LTspice:RFDBCK 3 33 RMOD 10K
Birologue 