3.1. Class2 Bond¶
3.1.1. Functional Form¶
The class 2 bond potential has the functional form:
\(E={{K}_{2,ij}}{{\left( {{R}_{ij}}-{{R}_{0,ij}} \right)}^{2}}+{{K}_{3,ij}}{{\left( {{R}_{ij}}-{{R}_{0,ij}} \right)}^{3}}+{{K}_{4,ij}}{{\left( {{R}_{ij}}-{{R}_{0,ij}} \right)}^{4}}\)
The force-field parameters for this potential and units are given by:
| Equation Symbol | Parameter Definition | Units |
| \(K_{2,ij}\) | Bond coefficient for atoms [i,j] (quadratic term) | energy/length^2 |
| \(K_{3,ij}\) | Bond coefficient for atoms [i,j] (cubic term) | energy/length^3 |
| \(K_{4,ij}\) | Bond coefficient for atoms [i,j] (quartic term) | energy/length^4 |
| \(R_{0,ij}\) | Equilibrium bond length for atoms [i,j] | length |
3.1.2. XML Schema¶
The XML schema for the class 2 bond 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 |
| Bond coefficient for atoms [i,j] (quadratic term) | \(K_{2,ij}\) | K2 |
| Bond coefficient for atoms [i,j] (cubic term) | \(K_{3,ij}\) | K3 |
| Bond coefficient for atoms [i,j] (quartic term) | \(K_{4,ij}\) | K4 |
| Equilibrium bond length for atoms [i,j] | \(R_{0,ij}\) | R0 |
The general attributes (describing the entire data set) are given by:
| General Attributes | Cardinality | Value/Definition |
| style | Fixed | Class2 |
| formula | Fixed | K2*(R-R0)^2+K3*(R-R0)^3+K4*(R-R0)^4 |
| K-units | Required | Enumerations specified in schema |
| R0-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.