4.2. Class2 Angle¶
4.2.1. Functional Form¶
The class 2 angle potential has the functional form:
\(E={{K}_{2,ijk}}{{\left( {{\theta }_{ijk}}-{{\theta }_{0,ijk}} \right)}^{2}}+{{K}_{3,ijk}}{{\left( {{\theta }_{ijk}}-{{\theta }_{0,ijk}} \right)}^{3}}+{{K}_{4,ijk}}{{\left( {{\theta }_{ijk}}-{{\theta }_{0,ijk}} \right)}^{4}}\)
The force-field parameters for this potential and units are given by:
| Equation Symbol | Parameter Definition | Units |
| \(K_{2,ijk}\) | Angle coefficient for atoms [i,j,k] (quadratic term) | energy/degrees^2 |
| \(K_{3,ijk}\) | Angle coefficient for atoms [i,j,k] (cubic term) | energy/degrees^3 |
| \(K_{4,ijk}\) | Angle coefficient for atoms [i,j,k] (quartic term) | energy/degrees^4 |
| \(\theta_{0,ijk}\) | Equilibrium angle for atoms [i,j,k] | degrees |
4.2.2. XML Schema¶
The XML schema for the class 2 angle 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 |
| Angle coefficient for atoms [i,j,k] (quadratic term) | \(K_{2,ijk}\) | K2 |
| Angle coefficient for atoms [i,j,k] (cubic term) | \(K_{3,ijk}\) | K3 |
| Angle coefficient for atoms [i,j,k] (quartic term) | \(K_{4,ijk}\) | K4 |
| Equilibrium angle for atoms [i,j,k] | \(\theta_{0,ijk}\) | Theta0 |
The general attributes (describing the entire data set) are given by:
| General Attributes | Cardinality | Value/Definition |
| style | Fixed | Class2 |
| formula | Fixed | K2*(Theta-Theta0)^2+K3*(Theta-Theta0)^3+K4*(Theta-Theta0)^4 |
| K-units | Required | Enumerations specified in schema |
| Theta0-units | Required | Enumerations specified in schema |
The specific attributes (attached to each set of parameters) are given by:
| Specific Attributes | Cardinality | Value/Definition |
| precedence | Optional | Precedence of parameter set (where specified) |
| 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.