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# Difference between revisions of "ISTART"

ISTART = 0 | 1 | 2 | 3

 Default: ISTART = 1 if a WAVECAR file exists = 0 else

Description: ISTART determines whether or not to read the WAVECAR file.

Start job: "begin from scratch". Initialize the orbitals according to the flag INIWAV.
Continuation job: "restart with constant energy cut-off". Orbitals are read from the WAVECAR file (usage is restricted in the parallel version). The set of plane waves will be redefined and re-padded according to the new cell size/shape (POSCAR) and the new plane wave cut-off (INCAR). These values might differ from the old values, that are stored in the WAVECAR file. If the WAVECAR file is missing or if the WAVECAR file contains an inappropriate number of bands and/or k-points the flag ISTART will revert to ISTART=0 (see above).
The usage of ISTART=1 is recommended if the size/shape of the supercell (see section on volume versus energy) or the cut-off energy changed with respect to the last run and if one wishes to redefine the set of plane waves according to a new setting.
ISTART=1 is the usual setting for convergence tests with respect to the cut-off energy and for all jobs where the volume/cell-shape varies (e.g. to calculate binding energy curves looping over a set of volumes).
Same as ISTART=2 but in addition a valid TMPCAR file must exist, containing the positions and orbitals at time steps ${\displaystyle t(N-1)}$ and ${\displaystyle t(N-2)}$, which are needed for the orbtial and charge prediction scheme (used for MD-runs).