7.2. Cross: Bond-Bond-13¶
7.2.1. Functional Form¶
The Bond-Bond-13 Cross Potential has the functional form:
\(E = {N} \left( {{R_{ij}} - {R_{1,ij}}} \right) \left( {{R_{kl}} - {R_{3,kl}}} \right)\)
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 |
| \(N\) | Cross potential bond coefficient for atoms [i,j,k,l] | energy |
| \(R_{1,ij}\) | Equilibrium bond length for atoms [i,j] | length |
| \(R_{3,kl}\) | Equilibrium bond length for atoms [k,l] | length |
7.2.2. XML Schema¶
The XML schema for the Bond-Bond-13 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] | \(N\) | N |
| Equilibrium bond length for atoms [i,j] | \(R_{1,ij}\) | R1 |
| Equilibrium bond length for atoms [k,l] | \(R_{3,kl}\) | R3 |
The general attributes (describing the entire data set) are given by:
| General Attributes | Cardinality | Value/Definition |
| style | Fixed | BondBond13 |
| formula | Fixed | N*(Rij-R1)*(Rkl-R3) |
| N-units | Required | Enumerations specified in schema |
| Ri-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.