IBRION: Difference between revisions
(Created page with '{{TAGDEF|IBRION|-1 {{!}} 0 {{!}} 1 {{!}} 2 {{!}} 3 {{!}} 5 {{!}} 6 {{!}} 7 {{!}} 8 {{!}} 44}} {{DEF|IBRION|-1|for {{TAG|NSW}}{{=}}−1 or 0|0|else}} Description: {{TAG|IBRIO…') |
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For {{TAG|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 ({{TAG|IBRION}}=2), which presently possesses the most reliable backup routines. Damped molecular dynamics ({{TAG|IBRION}}=3) are often useful when starting from very bad initial guesses. Close to the local minimum the RMM-DIIS ({{TAG|IBRION}}=1) is usually the best choice. {{TAG|IBRION}}=5 and {{TAG|IBRION}}=6 are using finite differences to determine the second derivatives (Hessian matrix and phonon frequencies), whereas {{TAG|IBRION}}=7 and {{TAG|IBRION}}=8 use density functional perturbation theory to calculate the derivatives. | For {{TAG|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 ({{TAG|IBRION}}=2), which presently possesses the most reliable backup routines. Damped molecular dynamics ({{TAG|IBRION}}=3) are often useful when starting from very bad initial guesses. Close to the local minimum the RMM-DIIS ({{TAG|IBRION}}=1) is usually the best choice. {{TAG|IBRION}}=5 and {{TAG|IBRION}}=6 are using finite differences to determine the second derivatives (Hessian matrix and phonon frequencies), whereas {{TAG|IBRION}}=7 and {{TAG|IBRION}}=8 use density functional perturbation theory to calculate the derivatives. | ||
* {{TAG|IBRION}}=-1 | * {{TAG|IBRION}}=-1: no update. | ||
:The ions are not moved, but {{TAG|NSW}} outer loops are performed. In each outer loop the electronic degrees of freedom are re-optimized (for {{TAG|NSW}}>0 this obviously does not make much sense, except for test purposes). If no ionic update is required use {{TAG|NSW}}=0 instead. | |||
* {{TAG|IBRION}}=0: molecular dynamics. | * {{TAG|IBRION}}=0: molecular dynamics. | ||
: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. {{TAG|POTIM}} supplies the timestep in femto seconds. The parameter {{TAG|SMASS}} provides additional control. | |||
:'''Mind''': At the moment only constant volume MD's are possible. | |||
* {{TAG|IBRION}}=1: ionic relaxation (RMM-DIIS). | * {{TAG|IBRION}}=1: ionic relaxation (RMM-DIIS). | ||
* {{TAG|IBRION}}=2: ionic relaxation (conjugate gradient algorithm). | * {{TAG|IBRION}}=2: ionic relaxation (conjugate gradient algorithm). | ||
Revision as of 12:31, 26 March 2011
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.
- IBRION=-1: no update.
- 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.
- IBRION=0: molecular dynamics.
- 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