the 3rd party model is self-contained as part of the schematic when you distribute the schematic file. The same .model can also be copied to an ASCII text file on your computer too, but it won't "travel" with a schematic when you copy it to another computer. For example, the following diode part numbers aren't included in the current LTspice device library: .model 1N4004_WIKI D(Is=500p Rs=0.12 N=1.6 Tt=4u Cjo=40p M=0.35 BV=400 Ibv=5.00u Mfg=BobCordellBook Type=Silicon) .model 1N4007_WIKI D(Is=7.02767n Rs=0.0341512 N=1.80803 Tt=1e-07 Cjo=1e-11 Vj=0.7 M=0.5 Eg=1.05743 Xti=5 Fc=0.5 BV=1000 Ibv=5e-08 Mfg=OnSemiconductor Type=Silicon) .model 1N5408_WIKI D(Is=63.0n Rs=14.1m N=1.70 Tt=4.32u Cjo=53.0p M=0.333 BV=1000 Ibv=10.0u Mfg=DiodesInc Type=Silicon) Number conventions In LTspice, numeric values can be expressed in four different ways: integer (i.e. 1000), real (i.e. 1000.0), scientific e-notation (i.e. 1e3, 1.0e3), scale factor notation (i.e. 1K, 1K0). If the first character after a number is not the letter "e" for scientific e-notation or a scale factor suffix (left column of table), then trailing characters are ignored. For example, 5 is treated the same as 5V / 5Volt / 5Volts / 5 Hz / 5Hertz. Scale factors Integer and real numbers supports a scale factor (multiplier) suffix. These are based mostly on metric conventions. The suffix (left column) can be upper / lower / mixed case, known as case insensitive. For example, 1MEG / 1meg / 1Meg represents 1000000; 1k / 1K represents 1000. Any appended text after the suffix (left column) is ignored. For example, 2MegHz / 2MegaOhm represents 2000000; 3mV / 3mOhm represents 0.003; 4uF / 4uHenry represents 0.000004. In LTspice, any suffix (left column) can replace the decimal point of a real number, a common format for printed schematics. For example, 4K7 represents 4700, 1u8 represents 0.0000018. Compatibility Although LTspice was originally based upon Berkeley SPICE 3f5 source code, it no longer is, thus some of its features may create non-portable files. Competitor SPICE programs have non-portable features too. LTspice features that may not be supported by some SPICE programs: Unicode characters in schematics, netlists, plot. This is a new feature in LTspice XVII, thus older versions of LTspice don't support Unicode. Unicode (U+00B5) µ micro character as an alternate symbol for ASCII (hex 75) u letter, which used as the micro (10−6) scale factor. See option setting at LTspice -> Tools -> Control Panel -> Netlist Options -> Convert 'µ' to 'u'. Unicode (U+2212) − minus character as an alternate symbol for