7.8. Cross: Angle-Angle-Torsion

7.8.1. Functional Form

The Angle-Angle-Torsion Cross Potential has the functional form:

\(E={{M}_{ijkl}}\left( {{\theta }_{ijk}}-{{\theta }_{1,ijk}} \right)\left( {{\theta }_{jkl}}-{{\theta }_{2,jkl}} \right)\cos \left( {{\phi }_{ijkl}} \right)\)

This term is part of the Class2 Dihedral Potential style.

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

Equation Symbol Parameter Definition Units
\(M_{ijkl}\) Bond coefficient for atoms [i,j,k,l] energy
\({\theta}_{1,ijk}\) Equilibrium angle for atoms [i,j,k] degrees
\({\theta}_{2,jkl}\) Equilibrium angle for atoms [j,k,l] degrees

7.8.2. XML Schema

The XML schema for the Angle-Angle-Torsion Cross Potential has the following representation (design mode representation using Liquid XML Studio):

../_images/Cross-AngleAngleTorsion.png

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
Bond coefficient for atoms [i,j,k,l] \(M_{ijkl}\) M
Equilibrium angle for atoms [i,j,k] \({\theta}_{1,ijk}\) Theta1
Equilibrium angle for atoms [j,k,l] \({\theta}_{2,jkl}\) Theta2

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

General Attributes Cardinality Value/Definition
style Fixed AngleAngleTorsion
formula Fixed M(Theta-Theta1)*(Theta-Theta2)*cos(Phi)
M-units Required Enumerations specified in schema
Theta-units Required Enumerations specified in schema

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

Specific Attributes Cardinality Value/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.