Spherical harmonic boundary conditions

NAMD provides spherical harmonic boundary conditions. These boundary conditions can consist of a single potential or a combination of two potentials as described in section 5.1.10. The following parameters are used to define these boundary conditions.

• sphericalBC $\langle$ use spherical boundary conditions? $\rangle$
  Acceptable Values: on or off
  Default Value: off
  Description: Specifies whether or not spherical boundary conditions are to be applied to the system. If set to on, then sphericalBCr1 and sphericalBCk1 must be defined, and sphericalBCexp1, sphericalBCr2, sphericalBCk2, and sphericalBCexp2 can optionally be defined.

• sphericalBCr1 $\langle$ radius for first boundary condition (Å) $\rangle$
  Acceptable Values: positive decimal
  Description: Distance at which the first potential of the boundary conditions takes effect. This distance is a radius from the center of mass.

• sphericalBCk1 $\langle$ force constant for first potential $\rangle$
  Acceptable Values: non-zero decimal
  Description: Force constant for the first harmonic potential. A positive value will push atoms toward the center of mass, and a negative value will pull atoms away from the center of mass.

• sphericalBCexp1 $\langle$ exponent for first potential $\rangle$
  Acceptable Values: positive, even integer
  Default Value: 2
  Description: Exponent for first boundary potential, most likely either 2 or 4.

• sphericalBCr2 $\langle$ radius for second boundary condition (Å) $\rangle$
  Acceptable Values: positive decimal
  Description: Distance at which the second potential of the boundary conditions takes effect. This distance is a radius from the center of mass. If this parameter is defined, then spericalBCk2 must also be defined.

• sphericalBCk2 $\langle$ force constant for second potential $\rangle$
  Acceptable Values: non-zero decimal
  Description: Force constant for the second harmonic potential. A positive value will push atoms toward the center of mass, and a negative value will pull atoms away from the center of mass.

• sphericalBCexp2 $\langle$ exponent for second potential $\rangle$
  Acceptable Values: positive, even integer
  Default Value: 2
  Description: Exponent for second boundary potential, most likely either 2 or 4.