H2O vibration: Difference between revisions

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*INCAR
*INCAR
SYSTEM = H2O vibration
<pre>
PREC = A
SYSTEM = H2O vibration
PREC = A
# IBRION = 1 ; NSW = 10 ; NFREE = 2 ; EDIFFG = -1E-4
# IBRION = 1 ; NSW = 10 ; NFREE = 2 ; EDIFFG = -1E-4
ENMAX = 400
ENMAX = 400
ISMEAR = 0    # Gaussian smearing
ISMEAR = 0    # Gaussian smearing
IBRION = 6    # finite differences with symmetry
IBRION = 6    # finite differences with symmetry
NFREE = 2    # central differences (default)
NFREE = 2    # central differences (default)
POTIM = 0.015 # default as well
POTIM = 0.015 # default as well
EDIFF = 1E-8  
EDIFF = 1E-8  
NSW = 1      # ionic steps > 0
NSW = 1      # ionic steps > 0
</pre>


*KPOINTS
*KPOINTS

Revision as of 17:39, 6 June 2012

  • INCAR
SYSTEM = H2O vibration
PREC = A
# 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, the drift in the forces is too large to obtain the zero frequency modes "exactly", and it is simplest to increase the cutoff ENCUT to 800 eV. The important and physically meaningful frequencies are, however, insensitive to the choice of the cutoff.

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1_8_H2Ovib.tgz


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