** Next:** Simulated annealing
** Up:** Examples
** Previous:** Dimers
** Contents**
** Index**

##

Molecular -- Dynamics

*About which files do you have to worry:*

INCAR
POSCAR
POTCAR
KPOINTS

For a molecular dynamics, we recommend the use of PREC=Normal,
although PREC=Low yields often satisfactory results.
Here an example INCAR file:
SYSTEM = Si
# electronic degrees
ENCUT = 120
LREAL = A # real space projection
PREC = Normal # chose Low only after tests
EDIFF = 1E-5 # do not use default (too large drift)
ISMEAR = -1 ; SIGMA = 0.172 # Fermi smearing: 2000 K 0.086 10-3
ALGO = Very Fast # recommended for MD (fall back ALGO = Fast)
MAXMIX = 40 # reuse mixer from one MD step to next
NCORE= 4 or 8 # one orbital on 4 cores
ISYM = 0 # no symmetry
NELMIN = 4 # minimum 4 steps per time step, avoid breaking after 2 steps
# MD (do little writing to save disc space)
IBRION = 0 ; NSW = 100 ; NWRITE = 0 ; LCHARG = .FALSE. ; LWAVE = .FALSE.
TEBEG = 2000 ; TEEND = 2000
# canonic (Nose) MD with XDATCAR updated every 50 steps
SMASS = 3 ; NBLOCK = 50 ; POTIM = 1.5
# micro canonical MD with temperature scaling every 50 steps
# good for equlibration but usually better to use Nose thermostat
#SMASS = -1 ; NBLOCK = 50 ; POTIM = 1.5

Use `ALGO=Very Fast` (RMM-DIIS for electrons) for large molecular dynamics runs.
One should also evaluate the projection operators in real space (`LREAL=A`)
to speed up the calculations, and it is recommended to use at least 4 electronic iterations per ionic step
(`NELMIN = 4`). For surface or difficult systems,
you might need to increase this value to `NELMIN = 8`.
Special consideration are required for the parameters `BMIX` and `MAXMIX`:
it is usually desirable to use optimal mixing parameters for
molecular dynamics simulations. This can be done by performing
a few static calculations with varying `AMIX` and `BMIX` parameters
and do determine the one leading to the fastest convergence.
However, in the current versions of VASP, the dielectric function
is reused when the ions are updated (an optimal `AMIX` and
`BMIX` is no longer that important). The dielectric function is
reused after ionic updates, if `MAXMIX` is set.
`MAXMIX` should be about three times as larger as
the number of iterations required
to converge the electronic orbitals in the first iteration.

After performing one MD run, it is possible to continue to run, by copying the
`CONTCAR` to `POSCAR` file and restarting VASP.
Since the `CONTCAR` file is written after every single step, it
is also possible to restart the molecular dynamics from a crashed run.

** Next:** Simulated annealing
** Up:** Examples
** Previous:** Dimers
** Contents**
** Index**
N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at