# Molecular Dynamics Simulations in VASP

I want to run molecular dynamics (MD) simulations with VASP for Mg2Si to investigate the simulation time vs ENCUT and KPOINTS, but I do not know how to set INCAR tags for example for the first run if ENCUT = 500 eV with 100fs time then should I change the value of ENCUT and time for the second run? What parameters of INCAR will remain the same to compare ENCUT with simulation time and to get one plot of energy convergence? If the first run goes well should I change my POSCAR too for the second run as input?

Thanks.

## MD input card for H2O molecule:

 # General tags
PREC   = Normal
ENCUT  = 400
ALGO   = Fast
LREAL  = Auto
ISMEAR = 0         # Gaussian smearing
SIGMA  = 0.05
ISYM   = 0         # Symmetry off

# MD related
IBRION = 0         # MD
POTIM  = 0.5       # Time step=0.5 fs
NSW    = 100       # Number of ionic steps
TEBEG  = 400       # Start temperature
TEEND  = 400       # Final temperature
SMASS  = 0         # Canonical (Nose-Hoover) thermostat
POMASS = 16.0  2.0 # Deuterium mass for Hydrogen

# Don’t write WAVECAR or CHGCAR
LWAVE  = F
LCHARG = F


## KPOINTS card for H2O molecule:

 KPOINTS (Gamma-only)
0
Gamma
1  1   1
0  0   0


Hope it helps.

• Thank you so much for your answer , so ENCUT will not change it will reamin constant as given in above format of INCAR now question arises Which value should I set for ENCUT as Mg2Si converges at 700 eV or it will be initial 500 eV for MD run? – Shalini Feb 23 at 9:07
• @Shalini [grep ENMAX POTCAR] ==> [ ENMAX = 126.143; ENMIN = 94.607 eV ENMAX = 245.345; ENMIN = 184.009 eV] I think ENCUT=400 is OK. Take a look at this: vasp.at/wiki/index.php/ENCUT – Jack Feb 23 at 9:16
• Yes I think ENCUT =400 is OK or may be I can try for another values to see changes and what about temperature I mean how one will decide this temp. range for particular system lets say Mg2Si in my case ? Thanks for discussion – Shalini Feb 23 at 9:30
• @Shalini Temperature is decided by what you want to investigate. – Jack Feb 23 at 10:43
• Okay so energy convergence what should be range high or low ? I want to investigate simulation time vs ENCUT and KPOINTS . – Shalini Feb 23 at 13:57