NELMDL
NELMDL = [integer]
| Default: NELMDL | = -5 | if ISTART=0, INIWAV=1, and IALGO=8 |
| = -12 | if ISTART=0, INIWAV=1, and IALGO=48 |
Description: NELMDL specifies the number of non-selfconsistent steps at the beginning.
If one initializes the orbitals randomly the initial orbitals are far from anything reasonable. The resulting charge density is also 'nonsense'. Therefore it makes sense to keep the initial Hamiltonian, which corresponds to the superposition of atomic charge densities, fixed during the first few steps.
Choosing a 'delay' for starting the charge density update becomes essential in all cases where the SC-convergence is very bad (e.g. surfaces or molecules/clusters, chains). Without setting a delay VASP will probably not converge or at least the convergence speed is slowed down.
NELMDL might be positive or negative. A positive number means that a delay is applied after each ionic movement (in general not a convenient option). A negative value results in a delay only for the start-configuration.