H2O vibration: Difference between revisions
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*INCAR | *INCAR | ||
SYSTEM = H2O vibration | SYSTEM = H2O vibration | ||
PREC = A | |||
# IBRION = 1 ; NSW = 10 ; NFREE = 2 ; EDIFFG = -1E-4 | |||
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- | EDIFF = 1E-8 | ||
NSW = 1 # ionic steps > 0 | NSW = 1 # ionic steps > 0 | ||
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*POSCAR | *POSCAR | ||
H2O _2 | 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 | How many zero frequency modes should be observed and why? | ||
Try to use the linear response code ({{TAG|IBRION}}=8 and {{TAG|EDIFF}}=1E-8) to obtain | |||
reference results. | |||
For finite differences, are the results sensitive to the step width {{TAG|POTIM}}. | |||
In this specific case, errors are too large at the default | |||
cutoff (drift in forces), and it is simplest to increase the | |||
cutoff {{TAG|ENCUT}} to 600 eV. The important and physically meaningful | |||
frequencies are however insensitive to the choice of the cutoff. | |||
== Download == | == Download == | ||
Revision as of 12:48, 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, 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
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