5.7. Quadratic Dihedral¶
5.7.1. Functional Form¶
The quadratic dihedral potential has the functional form:
\(E = {K_{d,ijkl}} \cdot \left( {{\phi_{ijkl}} - {\phi_{0,ijkl}}} \right)^2\)
The force-field parameters for this potential and units are given by:
Equation Symbol | Parameter Definition | Units |
\(K_{d,ijkl}\) | Dihedral coefficient for atoms [i,j,k,l] | energy/degrees^2 |
\(\phi_{0,ijkl}\) | Equilibrium Dihedral for atoms [i,j,k,l] | degrees |
5.7.2. XML Schema¶
The XML schema for the quadratic dihedral 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] | \(K_{d,ijkl}\) | Kd |
Equilibrium dihedral angle for atoms [i,j,k,l] | \(\phi_{0,ijkl}\) | Phi0 |
The general attributes (describing the entire data set) are given by:
General Attributes | Cardinality | Value |
style | Fixed | Quadratic |
formula | Fixed | Kd*(Phi_Phi0)^2 |
convention | Optional | Enumerations specified in schema |
Kd-units | Required | Enumerations specified in schema |
Phi0-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.