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DihedralFrom $1Table of contentsA dihedral angle is the angle that occurs between two planes defined by four atoms. Proper DihedralsA proper dihedral consists of four atoms, joined linearly through bonds. These dihedrals can be represented either by a periodic or Ryckaert-Bellemans potential.
Periodic DihedralsA periodic dihedral is represented by a cosine function of the form Vd(φijkl) = kφ(1 + cos(nφ - φs)) Ryckaert-Bellemans DihedralsThe form of a Ryckaert-Bellemans dihedral is given as Vrb(φijkl) = ΣCn(cos(ψ))n The above expression is evaluated for values of n from 0 to 5, and ψ is given as φ - 180°. Note that the OPLS force field uses a modified form of a Ryckaert-Bellemans dihedral, a Fourier function.
Improper DihedralsAn improper dihedral is used to keep planar groups (like rings) planar. This dihedral type can also be used to prevent interconversion of stereocenters.
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