nbonds <parameter-nbonds-statement> end

<parameter-nbonds-statement> :==

  cutnb=<real> 
  --{Nonbonded interaction cutoff for list generation.
     cutnb >= ctofnb + 2*tolerance. Default=8.5A}
  group|atom
  --{Exclusive flags: group by group or atom by atom cutoff. Default=atom}
  tolerance=<real>
  --{Distance that any atom is allowed to move before pairlist is 
     updated. Default=0.5A}
  wmin=<real>
  --{Close contact warning distance. Default=1.5A}
  inhibit=<real>
  --{Distance at which nonbonded interactions are truncated. Default=0.25A}
  special_position=<real> 
  --{Distance at which special positions are flagged. If less than 0 
     no special positions will be flagged. Default=0.1A}

  --{switching/shifting applies to both electrostatic and van der waals terms}
  --{========================================================================}

  ctofnb=<real>
  --{Distance at which the switching function or shifting function 
     makes the energy zero. Default=7.5A}
  ctonnb=<real>
  --{Distance at which the switching function becomes effective. Default=6.5A}
  truncation
  --{No switching or shifting. Energies are computed for atoms less then
     cutnb apart.}

  --{electrostatic options}
  --{=====================}

  switch
  --{Electrostatic switching function.}
  shift
  --{Electrostatic potential shifting function.}
  shforce
  --{Electrostatic force shifting function.}
  bshforce=<real>
  --{Constant for force shifting function. Default=1.0}
  eps=<real>
  --{Dielectric constant.}
  cdie
  --{Constant dielectric.}
  rdie
  --{R-dependent dielectric.}
  e14fac=<real>
  --{Scale factor for 1-4 electrostatic interactions.}

  --{van der Waals options}
  --{=====================}

  vswitch
  --{Enables vdw switching. Activating truncation will turn off switching.}
  repel=<real>
  --{If greater than 0, turns on repulsive potential & turns off
     electrostatics. The value specifies the factor to multiply the
     usual vdw radius by. Default=0}
  --{Repulsive term:
                                  irex   irex  rexp
     E   (R) =  Rcon*[(repel*Rmin)    - R     ]
      vdw
     where Rmin is the value at which the Lennard-Jones potential
     is minimal. Only irex=1,2 and rexp=2,4 are allowed.}
  rexponent=<integer>
  --{Exponent for repulsive potential. Default=2}
  irexponent=<integer>
  --{Internal exponent for repulsive potential. Default=2}
  rconst=<real>
  --{Force constant for repulsive potential. Default=100.0}

  --{attractive-repulsive term options}
  --{=================================}

  rattract=<real>
  --{Distance at which attractive-repulsive term energy well begins.}
  depthofwell=<real>
  --{Scale factor for depth of attractive-repulsive potential.}

  --{exclusion list options}
  --{======================}

  nbxmod=[+|-]1|[+|-]2|[+|-]3|[+|-]4|[+|-]5
  --{Mode for nonbonded exclusions:
       +-1=exclude nothing
       +-2=exclude only 1-2 (bond)
       +-3=exclude 1-2 (bond) and 1-3 (angle)
       +-4=exclude 1-2 1-3 and 1-4
       +-5=same as (4) but use special 1-4 parameters. 
     A positive mode value causes the explicit nonbonded exclusions (eg. in
     aromatic rings) to be added. A negative value causes them to be 
     discarded.}

  --{turning on/off energy terms}
  --{===========================}

  --{Use the flags command to enable/disable the energy terms:
       vdw - for van der waals (intra-molecular)
       elec - for electrostatic (intra-molecular)
       pvdw - for symmetry van der waals
       pele - for symmetry electrostatic.}