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Constrained molecular dynamics

- define the standard MD-related parameters:
`IBRION`=0, `TEBEG`, `POTIM`, `NSW`
- set
`MDALGO` to 1 or 2 for a simulation with Andersen, or Nose-Hoover
thermostat, respectively (check description of `ANDERSEN_PROB` and `SMASS`
for the thermostat-specific setting)
- define geometric constraints in file ICONST (see Sec. 6.62.4),
the input parameter
`STATUS` for constrained coordinates must be set to 0
- if the free-energy gradient is to be computed, set
`LBLUEOUT`=.TRUE.,
see Sec. 6.62.3

VASP can handle multiple (even redundant) constraints, note however that a too large number of constraints
can cause problems with the stability of the SHAKE algorithm. In the problematic cases, it is recommended
to use a looser convergence criterion and to allow a larger number of iterations in the SHAKE algorithm
(see Sec. 6.62.3).
The hard constraints can be used also in metadynamics simulations (`MDALGO`=1121).
Information about constraints is written in file REPORT, check the lines
following the string "Const_coord".

N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at