6.4. CVFF Improper¶
6.4.1. Functional Form¶
The CVFF improper potential has the functional form:
\(E={{K}_{i,ijkl}}\left[ 1+{{N}_{s}}\cos \left( N{{\phi }_{ijkl}} \right) \right]\)
The force-field parameters for this potential and units are given by:
| Equation Symbol | Parameter Definition | Units |
| \(K_{i,ijkl}\) | Dihedral coefficient for atoms [i,j,k,l] | energy |
| \(N_{s}\) | Determines sign convention (-1 or +1) | N/A |
| \(N\) | Nonnegative integer coefficient | N/A |
6.4.2. XML Schema¶
The XML schema for the CVFF improper 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 |
| Dihedral coefficient for atoms [i,j,k,l] | \(K_{i,ijkl}\) | K1 |
| Determines sign convention (-1 or +1) | \(N_{S}\) | Ns |
| Nonnegative integer coefficient | \(N\) | N |
The general attributes (describing the entire data set) are given by:
| General Attributes | Cardinality | Value |
| style | Fixed | CVFF |
| formula | Fixed | Ki*[1+Ns*cos(N*Phi)] |
| convention | Optional | Enumerations specified in schema |
| Ki-units | Required | Enumerations specified in schema |
| Chi0-units | Required | Enumerations specified in schema |
The specific attributes (attached to each set of parameters) are given by:
| Specific Attributes | Cardinality | 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.