atoms_dyn -ionic dynamics control variable

DESCRIPTION

The atoms_dyn variable determines the algorithm used to update atomic positions during a molecular dynamics run. The following values are allowed:
 

LOCKED: Ionic forces are not computed and atomic positions are not updated. This is the default.

 

SD: Steepest Descent. Ionic forces are computed and atomic positions are updated using the steepest descent algorithm:

    R(t+dt) = R(t) + F * dt² / m

where dt is the time step, F is the force and m is the ionic mass.
 

MD: Molecular Dynamics. Ionic forces are computed and atomic positions are updated using the Verlet algorithm:

    R(t+dt) = 2 * R(t) - R(t-dt) + F * dt² / m

If the pdamp variable is non-zero, a damping term is added to the Verlet dynamics as follows:

    R(t+dt) = R(t) + (1-pdamp) * (R(t) - R(t-dt)) + F * dt² / m
 

BMD: Blocking Molecular Dynamics. Ionic forces are computed and atomic positions are updated using the Verlet algorithm (with damping if pdamp > 0). The atoms' velocities are set to zero whenever the total energy is increasing.

 

LBFGS: Limited memory BFGS optimization algorithm. Requires a good convergence of the inner SC iterations for each atomic step. The inner SC iterations are stopped when sufficiently converged and forces are preconditioned according to the limited memory BFGS scheme.

If the LBFGS_hessian variable is set to a file name, the LBFGS procedure is initialized with the data in the specified file if it can be open and a restart file is written at the end of each run.

LBFGS References: D. Liu and J. Nocedal, "On the limited memory BFGS method for large scale optimization", Mathematical Programming B 45, p. 503-528 (1989). J. Nocedal, "Updating quasi-Newton matrices with limited storage", Mathematics of Computation, Vol.24, No.151, pp. 773-782 (1980).

 

LOCKED, SD, MD, BMD, LBFGS

DEFAULT VALUE

LOCKED

RELATED INFORMATION

wf_dyn, pdamp, thermostat