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):
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.