H2O vibration: Difference between revisions
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Latest revision as of 13:46, 14 November 2019
Overview > O atom > O atom spinpolarized > O atom spinpolarized low symmetry > O dimer > CO > CO vibration > CO partial DOS > H2O >
H2O vibration > H2O molecular dynamics > Further things to try > List of tutorials
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.