Molecular dynamics calculations: Difference between revisions
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*{{TAG|IBRION}}=0: Molecular dynamics calculations are enabled by setting the {{TAG|IBRION}} tag to 0. | *{{TAG|IBRION}}=0: Molecular dynamics calculations are enabled by setting the {{TAG|IBRION}} tag to 0. | ||
*{{TAG|MDALGO}}: This tag selects the type of thermostat used in the molecular dynamics calculations. For regular molecular dynamics calculations the thermostat is selected by a one digit number (e.g. 1 for Andersen, 2 for Nose-Hoover etc.). For biased molecular dynamics, metadynamics etc. the thermostat is selected by a two digit number where the first digit corresponds to the thermostat analogously to regular molecular dynamics and the second digit corresponds to the molecular dynamics type (e.g. 11 metadynamics with Andersen thermostat, 21 metadynamics with Nose-Hoover thermostat etc.). The NVE ensemble is a special case. It is available by selecting the Andersen thermostat and setting no collisions with the heat bath ({{TAG|ANDERSEN_PROB}}=0). | *{{TAG|MDALGO}}: This tag selects the type of thermostat used in the molecular dynamics calculations. For regular molecular dynamics calculations the thermostat is selected by a one digit number (e.g. 1 for Andersen, 2 for Nose-Hoover etc.). For biased molecular dynamics, metadynamics etc. the thermostat is selected by a two digit number where the first digit corresponds to the thermostat analogously to regular molecular dynamics and the second digit corresponds to the molecular dynamics type (e.g. 11 metadynamics with Andersen thermostat, 21 metadynamics with Nose-Hoover thermostat etc.). The NVE ensemble is a special case. It is available by selecting the Andersen thermostat and setting no collisions with the heat bath ({{TAG|ANDERSEN_PROB}}=0). | ||
*{{TAG|ISIF}}: The type of ensemble is chosen via this tag. For {{TAG|ISIF}}=2 the volume is kept constant and the NVT ensemble is used. Using this tag the stress tensor is calculated and hence the pressure can be monitored. For {{TAG|ISIF}}=3 the stress tensor (pressure) is kept constant and the NPT ensemble is used. Using this tag the volume is calculated and can be monitored. NVE | *{{TAG|ISIF}}: The type of ensemble is chosen via this tag. | ||
**For {{TAG|ISIF}}=2 the volume is kept constant and the {{TAG|NVT ensemble}} is used. Using this tag the stress tensor is calculated and hence the pressure can be monitored. | |||
**For {{TAG|ISIF}}=3 the stress tensor (pressure) is kept constant and the {{TAG|NPT ensemble}} is used. Using this tag the volume is calculated and can be monitored. | |||
**Calculations using the {{TAG|NVE ensemble}} are a special case. They are not controlled by the {{TAG|ISIF}} tag. A calculation in this ensemble can be achieved by setting setting {{TAG|ANDERSEN_PROB}}=0 (when {{TAG|MDALGO}}=1 is used) or setting {{TAG|SMASS}}=-3. | |||
== Combination of Ensembles and thermostats == | == Combination of Ensembles and thermostats == | ||
Revision as of 11:11, 3 June 2019
Compilation
First of all to run molecular dynamics calculation VASP has to be compiled using the -Dtbdyn precompiler flag in the makefile.include file. A sample input using this tag would look like this:
CPP = $(CPP_) -DHOST=\"IFC9_fftw\" \
-Dkind8 -DNGXhalf -DCACHE_SIZE=12000 -DPGF90 -Davoidalloc \
-Dtbdyn
Main INCAR tags
- IBRION=0: Molecular dynamics calculations are enabled by setting the IBRION tag to 0.
- MDALGO: This tag selects the type of thermostat used in the molecular dynamics calculations. For regular molecular dynamics calculations the thermostat is selected by a one digit number (e.g. 1 for Andersen, 2 for Nose-Hoover etc.). For biased molecular dynamics, metadynamics etc. the thermostat is selected by a two digit number where the first digit corresponds to the thermostat analogously to regular molecular dynamics and the second digit corresponds to the molecular dynamics type (e.g. 11 metadynamics with Andersen thermostat, 21 metadynamics with Nose-Hoover thermostat etc.). The NVE ensemble is a special case. It is available by selecting the Andersen thermostat and setting no collisions with the heat bath (ANDERSEN_PROB=0).
- ISIF: The type of ensemble is chosen via this tag.
- For ISIF=2 the volume is kept constant and the NVT ensemble is used. Using this tag the stress tensor is calculated and hence the pressure can be monitored.
- For ISIF=3 the stress tensor (pressure) is kept constant and the NPT ensemble is used. Using this tag the volume is calculated and can be monitored.
- Calculations using the NVE ensemble are a special case. They are not controlled by the ISIF tag. A calculation in this ensemble can be achieved by setting setting ANDERSEN_PROB=0 (when MDALGO=1 is used) or setting SMASS=-3.
Combination of Ensembles and thermostats
Thermostat Ensemble Andersen Nose-Hoover Langevin NHC CSVR Multiple Andersen Microcanonical (NVE) MDALGO=1, ANDERSEN_PROB=0.0 Canonical (NVT) MDALGO=1 MDALGO=2 MDALGO=3 MDALGO=4 MDALGO=5 MDALGO=13 ISIF=2 ISIF=2 ISIF=2 ISIF=2 ISIF=2 ISIF=2 Isobaric-isothermal (NpT) not available not available MDALGO=3 not available not available not available ISIF=3 Isoenthalpic-isobaric (NpH) MDALGO=3, ISIF=3, LANGEVIN_GAMMA=LANGEVIN_GAMMA_L=0.0