5.6. OPLS Dihedral

5.6.1. Functional Form

The OPLS dihedral potential has the functional forms:

\(E=\frac{1}{2}{{K}_{1,ijkl}}\left[ 1+\cos \left( {{\phi }_{ijkl}} \right) \right]+\frac{1}{2}{{K}_{2,ijkl}}\left[ 1-\cos \left( 2{{\phi }_{ijkl}} \right) \right]+\frac{1}{2}{{K}_{3,ijkl}}\left[ 1+\cos \left( 3{{\phi }_{ijkl}} \right) \right]\) \(\qquad +\frac{1}{2}{{K}_{4,ijkl}}\left[ 1-\cos \left( 4{{\phi }_{ijkl}} \right) \right]\)

The force-field parameters for this potential and units are given by:

Equation Symbol Parameter Definition Units
\(K_{1,ijkl}\) Dihedral coefficient for atoms [i,j,k,l] energy
\(K_{2,ijkl}\) Dihedral coefficient for atoms [i,j,k,l] energy
\(K_{3,ijkl}\) Dihedral coefficient for atoms [i,j,k,l] energy
\(K_{4,ijkl}\) Dihedral coefficient for atoms [i,j,k,l] energy

5.6.2. XML Schema

The XML schema for the OPLS dihedral potential has the following representation (design mode representation using Liquid XML Studio):


The relationship between the equation symbols and XML schema notations are given by:

Parameter Definition Equation Symbol Schema Notation
Atom type of atom [i] \(i\) AT-1
Atom type of atom [j] \(j\) AT-2
Atom type of atom [k] \(k\) AT-3
Atom type of atom [l] \(l\) AT-4
Dihedral coefficient for atoms [i,j,k,l] \(K_{1,ijkl}\) K1
Dihedral coefficient for atoms [i,j,k,l] \(K_{2,ijkl}\) K2
Dihedral coefficient for atoms [i,j,k,l] \(K_{3,ijkl}\) K3
Dihedral coefficient for atoms [i,j,k,l] \(K_{4,ijkl}\) K4

The general attributes (describing the entire data set) are given by:

General Attributes Cardinality Value
style Fixed OPLS
formula Fixed 0.5*{K1*[1+cos(Phi)]+K2*[1-cos(2*Phi)]+K3*[1+cos(3*Phi)]+K4*[1-cos(4*Phi)]}
convention Optional Enumerations specified in schema
Kn-units Required Enumerations specified in schema

The specific attributes (attached to each set of parameters) are given by:

Specific Attributes Cardinality Definition
comment Optional Comment attached to parameter set
version Optional Version number of parameter set
reference Optional Reference attached to parameter set

Note that an XML document will be rejected from being entered into the WebFF database if a required attribute is left unspecified.