Energy Minimization

Conjugate gradient parameters

The default minimizer uses a sophisticated conjugate gradient and line search algorithm with much better performance than the older velocity quenching method. The method of conjugate gradients is used to select successive search directions (starting with the initial gradient) which eliminate repeated minimization along the same directions. Along each direction, a minimum is first bracketed (rigorously bounded) and then converged upon by either a golden section search, or, when possible, a quadratically convergent method using gradient information.

For most systems, it just works.

• minimization $<$ Perform conjugate gradient energy minimization? $>$
  Acceptable Values: on or off
  Default Value: off
  Description: Turns efficient energy minimization on or off.

• minTinyStep $<$ first initial step for line minimizer $>$
  Acceptable Values: positive decimal
  Default Value: 1.0e-6
  Description: If your minimization is immediately unstable, make this smaller.

• minBabyStep $<$ max initial step for line minimizer $>$
  Acceptable Values: positive decimal
  Default Value: 1.0e-2
  Description: If your minimization becomes unstable later, make this smaller.

• minLineGoal $<$ gradient reduction factor for line minimizer $>$
  Acceptable Values: positive decimal
  Default Value: 1.0e-4
  Description: Varying this might improve conjugate gradient performance.

Velocity quenching parameters

You can perform energy minimization using a simple quenching scheme. While this algorithm is not the most rapidly convergent, it is sufficient for most applications. There are only two parameters for minimization: one to activate minimization and another to specify the maximum movement of any atom.

• velocityQuenching $<$ Perform old-style energy minimization? $>$
  Acceptable Values: on or off
  Default Value: off
  Description: Turns slow energy minimization on or off.

• maximumMove $<$ maximum distance an atom can move during each step (Å) $>$
  Acceptable Values: positive decimal
  Default Value: $0.75\times$cutoff$/$stepsPerCycle
  Description: Maximum distance that an atom can move during any single timestep of minimization. This is to insure that atoms do not go flying off into space during the first few timesteps when the largest energy conflicts are resolved.