Earlier AA simulations of RNTs utilized the OPLS 2005 FF, 28 so to be consistent, this FF was chosen for the AA simulations. The Optimized Potentials for Liquid Simulations (OPLS) FF was developed in the late 1990s by Dr. William L. Jorgensen at Purdue University, and again later at Yale University. It was developed and optimized to fit the experimental parameters of liquids, such as the heat of vaporization. The functional form of OPLS is characterized by the sum of the different types of internal energies: