E	potential energy	(kJ mol−1)
k b	force constant for bond stretching	(kJ mo−1 m−2)
kθ	force constant for angle bending	(kJ mo−1 rad−2)
q	partial atomic charge	(e)
r	distance	(m)
Greeks
ε	depth of potential	(kJ mol−1)
ε 0	vacuum permittivity	(=8.85 × 10−12 F m−1)
θ	bonding angle	(rad)
σ	distance at zero-potential energy	(m)
Subscripts
0	original position
i	component i
ij	pair of atoms i and j