In this study, we extend the OPPES united atom force field to normal alcohols, glycols, and alkoxyethanols by optimizing new

potential parameters based on the previously developed OPPES n-alkane and ether models. Bonded interaction parameters

were primarily adopted from the TraPPE-UA model, except for equilibrium bond lengths and bending angles, which were

obtained through density functional theory (DFT) geometry optimizations. Partial charges for ether oxygens and neighboring

carbon pseudo-atoms were taken from the OPPES ether model, while those for hydroxyl oxygens and hydrogens were

adopted from the AMBER model. The alpha carbon's charge was determined by enforcing charge neutrality. Lennard–Jones

(LJ) parameters for hydroxyl oxygen and hydrogen were fitted to experimental liquid densities and vapor pressures of

representative n-alcohols. Using the optimized parameters, we performed configurational-bias Monte Carlo simulations in

the NVT ensemble for five n-alcohols (methanol to 1-octanol), two glycols (1, 2-ethanediol and 1,3-propanediol), and three

alkoxyethanols (2-methoxyethanol to 2-propoxyethanol). Additionally, NPT Gibbs ensemble Monte Carlo simulations were

conducted for a binary n-heptane + 2-propoxyethanol system to evaluate phase behavior and local composition enhancements.

Hydrogen bonding statistics were analyzed to assess the model’s performance in capturing associative interactions and fluid

structure. Overall, the OPPES model yielded improved predictions of thermophysical properties compared to the TraPPE-UA

model, especially near critical conditions, demonstrating its potential as a reliable and transferable force field for associating

fluids.