O dimer: Difference between revisions

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*The CG algorithm requires line minimizations along the search direction. This is done using a variant of Brent's algorithm. (Picture missing)
*The CG algorithm requires line minimizations along the search direction. This is done using a variant of Brent's algorithm. (Picture missing)
**Trial step along search direction (gradient scaled by {{TAG|POTIM}})
**Trial step along search direction (gradient scaled by {{TAG|POTIM}})
**Quadratic or cubic interpolation using energies and forces at <math> \mathbf{x}_{0} </math> and <math> \mathbf{x}_{1} </math> allows to determine the approximate minimum
**Quadratic or cubic interpolation using energies and forces at <math> \mathbf{x}_{0} </math> and <math> \mathbf{x}_{1} </math> allows to determine the approximate minimum

Revision as of 13:14, 27 April 2017

Task

Relaxation of the bond length of an dimer.

Input

POSCAR

O dimer in a box
 1.0          ! universal scaling parameters
 8.0 0.0 0.0  ! lattice vector  a(1)
 0.0 8.0 0.0  ! lattice vector  a(2)
 0.0 0.0 8.0  ! lattice vector  a(3)
2             ! number of atoms
cart          ! positions in cartesian coordinates
 0 0 0        ! first atom
 0 0 1.22     ! second atom

INCAR

SYSTEM = O2 dimer in a box
ISMEAR = 0 ! Gaussian smearing
ISPIN  = 2 ! spin polarized calculation
NSW = 5    ! 5 ionic steps
IBRION = 2 ! use the conjugate gradient algorithm

KPOINTS

Gamma-point only
 0
Monkhorst Pack
 1 1 1
 0 0 0



Calculation

  • We have selected in the INCAR file that geometry relaxation should be performed. In this case 5 ionic steps (NSW=5) should be done at most. For the relaxation a conjugate gradient (CG) algorithm is used (IBRION=2).
  • The CG algorithm requires line minimizations along the search direction. This is done using a variant of Brent's algorithm. (Picture missing)
    • Trial step along search direction (gradient scaled by POTIM)
    • Quadratic or cubic interpolation using energies and forces at and allows to determine the approximate minimum
    • Continue minimization, if app. minimum is not accurate enough

Download

Odimer.tgz


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