Comparison of TIP5P water model and TIP4P water model in cluster nucleation kinetics study through umbrella sampling and free energy perturbation

The five-site potential functions (TIP5P water model) are descendants of the ST2 model, which involves a rigid water monomer with positive charges on two hydrogen H-sites, and negative charges on two M-sites mimicking the lone electron pair. In this paper, an efficient approach is described to compare the accuracy of TIP4P water model and TIP5P water model to determine the rates of elementary condensation and evaporation processes that lead to nucleation of aqueous aerosols. This approach started with the calculation of potential of mean force (PMF) through the trajectories of molecular dynamic simulation. The classical model potentials were corrected by ABC-FEP (ab initio/classical free energy perturbation). The calculated PMF was combined with classical nucleation theory and dynamical nucleation theory to calculate the evaporation rate constant (Kb), equilibrium constant (KEQ), and condensation rate constant (Kf). To test the feasibility of this approach, both dimer and trimer of TIP4P and TIP5P water models were used to calculate these values. The final results suggest that there is no obvious difference for TIP4P and TIP5P water model in water dimer. But classical model potential (Kb = 7.200 × 109, KEQ = 2.063 × 10−3, Kf = 1.485 × 107) is obviously different from the ABC-FEP corrected potential (Kb = 3.076 × 1010, KEQ = 4.979 × 10−4, Kf = 1.532 × 107) of TIP4P model. There is no difference between classical model potential (Kb = 3.717 × 1010, KEQ = 3.832 × 10−4, Kf = 1.424 × 107) and ABC-FEP corrected potential (Kb = 3.158 × 1010, KEQ = 4.565 × 10−4, Kf = 1.442 × 107) for TIP5P water model.