The first term in Eq. (2) is the bond-stretching potential, where
Kr is the bond-stretching energy coefficient,
r represents the bond length, and
r0 is the equilibrium bond length. The second term is the bond angle-bending potential, where
Kθ is the bond angle-bending energy coefficient,
θ represents the bond angle, and
θ0 is the equilibrium bond angle. The third term is the torsional (dihedral) potential, where
Kϕ is the torsion energy coefficient,
n is the multiphase factor, and
γ is the equilibrium dihedral angle. The fourth term is the van der Waals potential in the Lennard–Jones (LJ) in 6–12 form, where
εij is the traditional well-depth, and
σij is the distance between atoms
i and
j, at which the energy of the two atoms reaches zero and minimum, respectively. The LJ parameters for dissimilar atoms were obtained from the Lorentz–Berthelot combination rule, as expressed in Eq. (3). The fifth term is the electrostatic potential, where
qi and
qj denote the electrical charge of atoms
i and
j, respectively. The selected values of the parameters in the all-atom force field can be obtained from Ref. [
44].