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Relaxation of the bond length of an oxygen dimer.
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
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
Gamma-point only 0 Monkhorst Pack 1 1 1 0 0 0
- 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
DAV: 1 0.517118590134E+02 0.51712E+02 -0.31393E+03 80 0.366E+02 ... ... ... ... ... ... DAV: 14 -0.985349953776E+01 -0.15177E-03 -0.57546E-06 64 0.125E-02 0.371E-03 DAV: 15 -0.985357023804E+01 -0.70700E-04 -0.22439E-06 64 0.741E-03 1 F= -.98535702E+01 E0= -.98535702E+01 d E =-.985357E+01 mag= 2.0000 curvature: 0.00 expect dE= 0.000E+00 dE for cont linesearch 0.000E+00 trial: gam= 0.00000 g(F)= 0.113E+00 g(S)= 0.000E+00 ort = 0.000E+00 (trialstep = 0.100E+01) search vector abs. value= 0.113E+00 bond charge predicted ... ... ... ... ... ... 2 F= -.96234585E+01 E0= -.96234585E+01 d E =0.230112E+00 mag= 2.0000 trial-energy change: 0.230112 1 .order 0.190722 -0.113406 0.494850 step: 0.1397(harm= 0.1864) dis= 0.00731 next Energy= -9.861386 (dE=-0.782E-02) bond charge predicted ... ... ... ... ... ... 3 F= -.98607735E+01 E0= -.98607735E+01 d E =-.720327E-02 mag= 2.0000 curvature: -0.09 expect dE=-0.900E-05 dE for cont linesearch -0.900E-05 trial: gam= 0.00000 g(F)= 0.969E-04 g(S)= 0.000E+00 ort =-0.331E-02 (trialstep = 0.828E+00) search vector abs. value= 0.969E-04 reached required accuracy - stopping structural energy minimisation
Explanation of the output:
- The quantitiy trial-energy change is the change of the energy in the trial step.
- The first value after 1. order is the expected energy change calculated from the forces change of positions - central difference.
- The second and third value correspond to change of positions and change of position.
- The value step is the estimated size of the step leading to a line minimization along the current search direction. harm is the optimal step using a second order (or harmonic) interpolation.
- The trial step size can be controlled by the paramter POTIM (the value step times the present POTIM is usually optimal).
- The final positions after the optimization are stored in the CONTCAR file. One can copy CONTCAR to POSCAR and continue the relaxation.