Constant Forces

NAMD provides the ability to apply constant forces to some atoms. There are three parameters that control this feature.

• constantForce $<$ Apply constant forces? $>$
  Acceptable Values: yes or no
  Default Value: no
  Description: Specifies whether or not constant forces are applied.

• consForceFile $<$ PDB file containing forces to be applied $>$
  Acceptable Values: UNIX filename
  Description: The X, Y, Z and occupancy (O) fields of this file are read to determine the constant force vector of each atom, which is (X,Y,Z)*O, in unit of kcal/(mol*Å). The occupancy (O) serves as a scaling factor, which could expand the range of the force applied. (One may be unable to record very large or very small numbers in the data fields of a PDB file due to limited space). Zero forces are ignored.

  Specifying consforcefile is optional; constant forces may be specified or updated between runs by using the consForceConfig command.

• consForceScaling $<$ Scaling factor for constant forces $>$
  Acceptable Values: decimal
  Default Value: 1.0
  Description: Scaling factor by which constant forces are multiplied. May be changed between run commands.