As the title says, what does "the natural bond angle θ0" mean in the context of Universal Force Field (UFF) potential energy calculation? The reference appears in section D. Angular Distortions, 1. Angle Bend). The article also talks about "natural bond length" (Section C. Bond Stretch).
I am curious about how molecular dynamics (MD) simulations estimate/calculate bond angles using the Universal Force Field.
At several points in the original UFF paper they mention a "natural angle" but it is not overwhelmingly clear to me what this means. Is it the empirically observed bond angle(s) in particular molecules? How do MD simulations, then, produce bond angles for molecules that there is no published data for?
I understand that the UFF potential energy calculation contains several terms that account for various properties like hybridization, van der Waals interactions, etc. Which of the terms, which are outlined in the first pages, account(s) for steric interactions between molecules and determine the final bond angles?
I am admittedly not very well versed in the types of maths that are involved, but I would appreciate any explanation possible.
Thank you very much in advance!