Type:         String
  Default:      GEOMETRIC
  Definition:   [GEOMETRIC / HHG / W-H]
Selects the combining rule used to derive the epsilon value for van der Waals interactions.
The default in the absence of the epsilonrule keyword is to use the geometric mean of the
individual epsilon values of the two atoms involved in the van der Waals interaction.

  Type:         Double
  Default:      0.07
  Definition:   Sets the value of the delta parameter in Halgren’s buffered 14-7 vdw potential energy functional form.
In the absence of the delta-halgren property, a default value of 0.07 is used.

  Type:         Double
  Default:      0.12
  Definition:   Sets the value of the gamma parameter in Halgren’s buffered 14-7 vdw potential energy functional form.
In the absence of the gamma-halgren property, a default value of 0.12 is used."

  Type:         String
  Default:      ARITHMETIC
  Definition:   [ARITHMETIC / GEOMETRIC / CUBIC-MEAN]
Sets the functional form of the radius combining rule for heteroatomic van der Waals potential energy interactions.
The default in the absence of the radiusrule keyword is to use the arithmetic mean combining rule to get radii for heteroatomic interactions.

  Type:         String
  Default:      RADIUS
  Definition:   [RADIUS / DIAMETER]
Determines whether the atom size values given in van der Waals parameters read from
VDW keyword statements are interpreted as atomic radius or diameter values.
The default in the absence of the radiussize keyword is to assume that vdw size parameters are given as radius values.

  Type:         String
  Default:      R-MIN
  Definition:   [R-MIN / SIGMA]
Determines whether atom size values given in van der Waals parameters read from VDW keyword
statements are interpreted as potential minimum (Rmin) or LJ-style sigma values.
The default in the absence of the radiustype keyword is to assume that vdw size parameters are given as Rmin values.

  Type:         Double
  Default:      0.0
  Definition:   Provides a multiplicative scale factor that is applied to van der Waals potential
interactions between 1-2 connected atoms, i.e., atoms that are directly bonded.
The default value of 0.0 is used to omit 1-2 interactions,
if the vdw-12-scale property is not given in either the parameter file or the property file.

  Type:         Double
  Default:      0.0
  Definition:   Provides a multiplicative scale factor that is applied to van der Waals potential
interactions between 1-3 connected atoms, i.e., atoms separated by two covalent bonds.
The default value of 0.0 is used to omit 1-3 interactions, if the vdw-13-scale property
is not given in either the parameter file or the property file.

  Type:         Double
  Default:      1.0
  Definition:   Provides a multiplicative scale factor that is applied to van der Waals potential
interactions between 1-4 connected atoms, i.e., atoms separated by three covalent bonds.
The default value of 1.0 is used, if the vdw-14-scale keyword is not given in either
the parameter file or the property file.

  Type:         String
  Default:      class
  Definition:   [CLASS / TYPE]
Specifies whether van der Waals parameters are provided for atom classes or atom types.
While most force fields are indexed by atom class, in OPLS models the vdW values are indexed by atom type.
The default in the absence of the vdwindex property is to index vdW parameters by atom class.

  Type:         String
  Default:      LENNARD-JONES
  Definition:   [LENNARD-JONES / BUFFERED-14-7]
Sets the functional form for the van der Waals potential energy term.
The text modifier gives the name of the functional form to be used.
The default in the absence of the vdwtype keyword is to use the standard two parameter Lennard-Jones function.