LT Spice

Types of files:

1. library files - .lib (SPICE file)
• .model file that are for intrinsic devices like diodes and transistors
• .sub or .subckt file are for subcircuit components like opamps that are made up of diodes and transistors
2. symbol file - .asy

Adding third party model to LT Spice:

http://www.linear.com/solutions/1083 

Adding a PSpice model of any thrid party vendor to LTSpice:

Example: TLV2316 opamp

• Open the spice model file of component TLV316.cir or TLV316.txt
• Copy the SPICE model name TLV316 from .subckt TLV316 IN+ IN- VCC VEE OUT
• Open LTSpice and Add component symbol: Component->opamp->Universal opamp 
• Right click on the component and Add SPICE model name to SPICEModel
• Open SPICE Direcetive and add command: 

.lib D:\ingodbsu\Documents\LTspiceXVII\lib\user_addition\TLV2316\TLV316.txt

• Set the simulation command
• Save it and you are done