Force values for AIMD calculation

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tisita_das
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Force values for AIMD calculation

#1 Post by tisita_das » Mon Sep 26, 2022 6:30 am

Dear Experts,

How do we get force value printed for each ionic step relaxation for AIMD calculation in VASP?

Actually I have run a MD simulation calculation on Pt(111)/water surface for 10 ps with 1 fs time step using VASP. After optimization I found that, in the OUTCAR file the force value is printed only for first and last ionic step relaxation. But I need the force value and stress tensors for each of the steps. Is there any way to resolve this? Do I need to use any particular tag in INCAR which writes forces for each of the ionic steps or is there other file from which we can extract the forces for individual step?

The INCAR file of my calculation is as follows:

Global Parameters
ISTART = 0 (Read existing wavefunction; if there)
ISPIN = 1 (Non-Spin polarised DFT)
ICHARG = 2 (Non-self-consistent: GGA/LDA band structures)
LREAL = Auto (Projection operators: automatic)
ENCUT = 500 (Cut-off energy for plane wave basis set, in eV)
PREC = Normal (Precision level)
LWAVE = .FALSE. (Write WAVECAR or not)
LCHARG = .FALSE. (Write CHGCAR or not)
#ADDGRID= .TRUE. (Increase grid; helps GGA convergence)
NPAR = 4 (Max is no. nodes; don't set for hybrids)
#KPAR = (Divides k-grid into separate groups)

Electronic Relaxation
ISMEAR = 0
SIGMA = 0.1
EDIFF = 1E-04

Molecular Dynamics
IBRION = 0 (Activate MD)
NSW = 10000 (Max ionic steps)
#EDIFFG = -1E-02 (Ionic convergence; eV/A)
POTIM = 1 (Timestep in fs)
MDALGO = 2
SMASS = 1 (MD Algorithm: -3-microcanonical ensemble; 0-canonical ensemble)
TEBEG = 300 (Start temperature K)
TEEND = 300 (Final temperature K)
ISYM = 0 (Switch symmetry off)
Nwrite = 0 (For long MD-runs use Nwrite=0 or Nwrite=1)
SYMPREC = 1E-8
LVTOT = .TRUE.

Any suggestions/comments will be helpful
Thanks in advance.

ferenc_karsai
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Re: Force values for AIMD calculation

#2 Post by ferenc_karsai » Mon Sep 26, 2022 6:36 am

You have set NWRITE=0. This means that the forces are written only in the first and last step.
NWRITE=1 would write forces at every step.
Please look at the documentation of NWRITE:
https://www.vasp.at/wiki/index.php/NWRITE

tisita_das
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Re: Force values for AIMD calculation

#3 Post by tisita_das » Mon Sep 26, 2022 6:53 am

Okay I have got it now. Thank you for your prompt respons ferenc_karsai.

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