H2O vibration: Difference between revisions

From VASP Wiki
Line 53: Line 53:
== Download ==
== Download ==
[http://www.vasp.at/vasp-workshop/examples/H2Ovib.tgz H2Ovib.tgz]
[http://www.vasp.at/vasp-workshop/examples/H2Ovib.tgz H2Ovib.tgz]
----
[[:Category:Tutorials |To the list of tutorials]] or to the [[The_VASP_Manual|main page]]
{{Template:At_and_mol}}
 
Back to the [[:Category:Tutorials |list of tutorials]] or to the [[The_VASP_Manual|main page]]
 
[[Category:Examples]]
[[Category:Examples]]

Revision as of 15:13, 9 August 2017

Task

Calculation of the vibrational frequencies of a molecule.

Input

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

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
 0
Monkhorst Pack
 1 1 1
 0 0 0

Calculation

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.

Download

H2Ovib.tgz

Back to the list of tutorials or to the main page