Molecular dynamics calculations: Difference between revisions

Revision as of 11:36, 29 May 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. NVE is again a special case since the thermostat is simply turned off by setting ANDERSEN_PROB=0.

Combination of Ensembles and thermostats

	Thermostat
Ensemble	Andersen	Nose-Hoover	Langevin	Multiple Andersen
Microcanonical (NVE)	MDALGO=1, ANDERSEN_PROB=0.0
Canonical (NVT)	MDALGO=1	MDALGO=2	MDALGO=3	MDALGO=13
	ISIF=2	ISIF=2	ISIF=2	ISIF=2
Isobaric-isothermal (NpT)	not available	not available	MDALGO=3	not available
			ISIF=3
Isoenthalpic-isobaric (NpH)	MDALGO=3, ISIF=3, LANGEVIN_GAMMA=LANGEVIN_GAMMA_L=0.0

@@ Line 8: / Line 8: @@
 *{{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|ISIF}}: This tag controls which type of ensemble is chosen (NVE, NVT or NPT).
+*{{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 is again a special case since the thermostat is simply turned off by setting {{TAG|ANDERSEN_PROB}}=0.
 == Combination of Ensembles and thermostats ==