wf_dyn -wavefunctions dynamics control variable

DESCRIPTION

The wf_dyn variable determines the algorithm used to update electronic wavefunctions during a molecular dynamics run, or during a minimization of the electronic energy. The following values are allowed:
 

• LOCKED: Wavefunctions are not updated.

 
• SD: Steepest Descent. This is the default. Wavefunctions are updated using a steepest descent algorithm:

 
psi(t+dt) = psi(t) + (dt² / emass) * H psi(t)


where dt is the time step, H is the hamiltonian and emass is the fictitious electronic mass.
 

• PSD: Preconditioned Steepest Descent. Wavefunctions are updated using a preconditioned Steepest Descent algorithm. The preconditioner is determined by the value of the ecutprec variable.

 
• PSDA: Preconditioned Steepest Descent with Anderson extrapolation. Uses the same preconditioned Steepest Descent directions as in PSD. Computes extrapolation coefficients according to Anderson's algorithm to minimize the norm of the preconditioned steepest descent vector in the subspace defined by the vectors at the current and the previous iteration.
  
   
• PSD_E: Preconditioned Steepest Descent for Empty states only. Wavefunctions  are updated using a preconditioned Steepest Descent algorithm. The Coulomb and exchange-correlation potentials are recomputed only when ions are moved. This allows for a faster calculation of empty electronic states when occupied states are already computed to sufficient accuracy. Example: 
  
    # assume that wavefunctions for occupied states are converged
   set wf_dyn PSD_E
    run 1 100
  
  The electronic states are updated 100 times without recomputing the Coulomb and exchange-correlation potentials.

 

 

• MD: Molecular Dynamics. Wavefunctions are updated using the Verlet algorithm:


      psi(t+dt) = 2 * psi(t) - psi(t-dt) + (dt² / emass) * H psi(t)

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

      psi(t+dt) = psi(t) + (1-edamp) * (psi(t)-psi(t-dt)) +

(dt² / emass) * H psi(t)


A damping term can be used to reach the electronic ground state in a minimization of the electronic energy.
 

• BMD: Blocking Molecular Dynamics. Wavefunctions are updated using the Verlet algorithm (with damping if edamp> 0). The wavefunctions' velocities are set to zero whenever the total energy is increasing.

 

LOCKED, SD, PSD, PSDA, MD, BMD

DEFAULT VALUE

SD

RELATED INFORMATION

edamp, ecutprec