H2O vibration: Difference between revisions
No edit summary |
|||
| (18 intermediate revisions by 3 users not shown) | |||
| Line 1: | Line 1: | ||
{{Template:At_and_mol - Tutorial}} | |||
== Task == | |||
Calculation of the vibrational frequencies of a <math>\mathrm{H}_{2}\mathrm{O}</math> molecule. | |||
== Input == | |||
=== {{TAG|POSCAR}} === | |||
<pre> | |||
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 | |||
</pre> | |||
=== {{TAG|INCAR}} === | |||
{{TAGBL|SYSTEM}} = H2O vibration | |||
{{TAGBL|PREC}} = A | |||
# {{TAGBL|IBRION}} = 1 ; {{TAGBL|NSW}} = 10 ; {{TAGBL|NFREE}} = 2 ; {{TAGBL|EDIFFG}} = -1E-4 | |||
{{TAGBL|ENMAX}} = 400 | |||
{{TAGBL|ISMEAR}} = 0 # Gaussian smearing | |||
{{TAGBL|IBRION}} = 6 # finite differences with symmetry | |||
{{TAGBL|NFREE}} = 2 # central differences (default) | |||
{{TAGBL|POTIM}} = 0.015 # default as well | |||
{{TAGBL|EDIFF}} = 1E-8 | |||
{{TAGBL|NSW}} = 1 # ionic steps > 0 | |||
=== {{TAG|KPOINTS}} === | |||
Gamma-point only | Gamma-point only | ||
0 | |||
Monkhorst Pack | |||
0 0 0 | 1 1 1 | ||
0 0 0 | |||
== Calculation == | |||
How many zero frequency modes should be observed and why? | How many zero frequency modes should be observed and why? | ||
| Line 33: | Line 46: | ||
reference results. | reference results. | ||
For finite differences, are the results sensitive to the step width {{TAG|POTIM}}. | For finite differences, are the results sensitive to the step width {{TAG|POTIM}}. | ||
In this specific case, | 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 {{TAG|ENCUT}} to | cutoff {{TAG|ENCUT}} to 800 eV. The important and physically meaningful | ||
frequencies are however insensitive to the choice of the cutoff. | frequencies are, however, insensitive to the choice of the cutoff. | ||
== Download == | == Download == | ||
[ | [[Media:H2Ovib.tgz| H2Ovib.tgz]] | ||
{{Template:At_and_mol}} | |||
[[Category:Examples]] | [[Category:Examples]] | ||
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.