8.13. Non-Bond Weeks-Chandler-Anderson Potential¶
8.13.1. Functional Form¶
The non-bond Weeks-Chandler-Anderson potential has the functional form:
\(E=4\epsilon \left[ {{\left( \frac{{{\sigma }_{ij}}}{{{R}_{ij}}} \right)}^{12}}-{{\left( \frac{{{\sigma }_{ij}}}{{{R}_{ij}}} \right)}^{12}}+\frac{1}{4} \right]\)
The force-field parameters for this potential and units are given by:
| Equation Symbol | Parameter Definition | Units |
| \(\epsilon\) | Potential well depth for atom [i] | energy/mol |
| \(\sigma\) | Interatomic cut-off distance for atom [i] | length |
8.13.2. XML Schema¶
The XML schema for the non-bond Weeks-Chandler-Anderson 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] | (implicit) | AT-1 |
| Atom type of atom [j] | (implicit) | AT-2 |
| Potential well depth for atom [i] | \(\epsilon\) | epsilon |
| Interatomic cut-off distance for atom [i] | \(\sigma\) | sigma |
| Interatomic cut-off distance for atom [i] | N/A | r_cut |
The general attributes (describing the entire data set) are given by:
| General Attributes | Cardinality | Value/Definition |
| style | Fixed | Weeks-Chandler-Anderson |
| formula | Fixed | 4*epsilon*[((sigma/R)^-12)-((sigma/R)^-6)+(1/4)] |
| epsilon-units | Required | Enumerations specified in schema |
| sigma-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.