H2O vibration

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Revision as of 12:48, 6 June 2012 by Kresse (talk | contribs)
  • INCAR
SYSTEM = H2O vibration
PREC = A
  1. IBRION = 1 ; NSW = 10 ; NFREE = 2 ; EDIFFG = -1E-4
ENMAX = 400
ISMEAR = 0    # Gaussian smearing
IBRION = 6    # finite differences with symmetry
NFREE = 2     # central differences (default)
POTIM = 0.015 # default as well
EDIFF = 1E-8 
NSW = 1       # ionic steps > 0
  • KPOINTS
Gamma-point only
 1        ! one k-point
rec       ! in units of the reciprocal lattice vector
 0 0 0 1  ! 3 coordinates and weight
  • POSCAR
H2O _2                                                                          
1.0000000
  8.0000000   0.0000000   0.0000000
  0.0000000   8.0000000   0.0000000
  0.0000000   0.0000000   8.0000000
   1    2

cart

  0.0000000   0.0000000   0.0000000
  0.5960812  -0.7677068   0.0000000
  0.5960812   0.7677068   0.0000000

How many zero frequency modes should be observed and why? Try to use the linear response code (IBRION=8 and EDIFF=1E-8) to obtain reference results. For finite differences, are the results sensitive to the step width POTIM. In this specific case, errors are too large at the default cutoff (drift in forces), and it is simplest to increase the cutoff ENCUT to 600 eV. The important and physically meaningful frequencies are however insensitive to the choice of the cutoff.

Download

1_8_H2Ovib.tgz


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