ISYM-tag and SYMPREC-tag

ISYM= -1 | 0 | 1 | 2 | 3

switch symmetry on (ISYM=1, 2 or 3) or off (ISYM=-1 or 0). For ISYM=2 a more efficient, memory conserving symmetrisation of the charge density is used. This reduces memory requirements in particular for the parallel version.

ALGO-tagALGO = Normal | VeryFast | Fast | Conjugate | All | Damped | Subrot | Eigenval | None | Nothing | Exact | Diag

The ALGO tag is a convenient option to specify the electronic minimisation algorithm in VASP.4.5 and later versions. Except for ``None'' and ``Nothing'', ``Exact'' and ``Diag'' (which must be spelled out), the first letter determines the applied algorithm. Conjugate, Subrot, Eigenval, Exact, None and Nothing are only supported by VASP.5.2.12 and newer versions.

ALGO = Normal selects IALGO = 38 (blocked Davidson iteration scheme), whereas ALGO = Very_Fast selects IALGO = 48 (RMM-DIIS). A faily robust mixture of both algorithm is selected for ALGO = Fast. In this case, Davidson (IALGO = 38) is used for the initial phase, and then VASP switches to RMM-DIIS (IALGO = 48). Subsequencly, for each ionic update, one IALGO = 38 sweep is performed for each ionic step (except the first one).

IALGO, and LDIAG-tagIALGO = 38 | 48         LDIAG = .TRUE. | .FALSE.

IALGO = integer selecting algorithmLDIAG = perform sub space rotation

Please mind, that the VASP.4.5 default is IALGO = 38 (a Davidson block iteration scheme). IALGO = 8 is not supported for copyright reasons in VASP.4.5, but IALGO = 38 is roughly 2 times faster for large systems than IALGO = 8 and at least as stable.