IBRION

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Revision as of 12:31, 26 March 2011 by Mmars (talk | contribs)

IBRION = -1 | 0 | 1 | 2 | 3 | 5 | 6 | 7 | 8 | 44 

Default: IBRION = -1 for NSW=−1 or 0
= 0 else

Description: IBRION determines how the ions are updated and moved.


For IBRION=0, a molecular dynamics is performed, whereas all other algorithms are destined for relaxations into a local energy minimum. For difficult relaxation problems it is recommended to use the conjugate gradient algorithm (IBRION=2), which presently possesses the most reliable backup routines. Damped molecular dynamics (IBRION=3) are often useful when starting from very bad initial guesses. Close to the local minimum the RMM-DIIS (IBRION=1) is usually the best choice. IBRION=5 and IBRION=6 are using finite differences to determine the second derivatives (Hessian matrix and phonon frequencies), whereas IBRION=7 and IBRION=8 use density functional perturbation theory to calculate the derivatives.

The ions are not moved, but NSW outer loops are performed. In each outer loop the electronic degrees of freedom are re-optimized (for NSW>0 this obviously does not make much sense, except for test purposes). If no ionic update is required use NSW=0 instead.
Standard ab-initio molecular dynamics. A Verlet algorithm (or fourth-order predictor-corrector if VASP was linked with stepprecor.o) is used to integrate Newton's equations of motion. POTIM supplies the timestep in femto seconds. The parameter SMASS provides additional control.
Mind: At the moment only constant volume MD's are possible.
  • IBRION=1: ionic relaxation (RMM-DIIS).
  • IBRION=2: ionic relaxation (conjugate gradient algorithm).
  • IBRION=3: ionic relaxation (damped molecular dynamics).
  • IBRION=5 and 6: second derivatives, Hessian matrix and phonon frequencies (finite differences).
  • IBRION=7 and 8: second derivatives, Hessian matrix and phonon frequencies (perturbation theory).
  • IBRION=44

Related Tags and Sections

NSW, SMASS


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