IALGO

IALGO = -1 | 2-4 | 5-8 | 15-18 | 28 | 38 | 44-48 | 53-58

Default: IALGO	= 8	for VASP.4.4 and older
	= 38	else (if ALGO is not set)

Description: IALGO selects the algorithm used to optimize the orbitals.

Mind: We strongly urge the users to select the algorithms via ALGO. Algorithms other than those available via ALGO are subject to instabilities.

IALGO=-1: Performance test.

VASP does not perform an actual calculation, only some important parts of the program will be executed and the timing for each part is printed out at the end.

IALGO=5-8: Conjugate gradient algorithms.

Optimize each band iteratively using a conjugate gradient algorithm. Subspace-diagonalization before conjugate gradient algorithm. The conjugate gradient algorithm is used to optimize the eigenvalue of each band.

IALGO=5 steepest descent
IALGO=6 conjugated gradient
IALGO=7 preconditioned steepest descent
IALGO=8 preconditioned conjugated gradient

IALGO=8 (VASP-releases older than VASP.4.5) is always fastest, IALGO=5-7 are only implemented for test purposes.

Please mind, that IALGO=8 is not supported as of VASP.4.5, since M. Teter, Corning and M. Payne hold a patent on this algorithm.

IALGO=38: Blocked-Davidson algorithm (ALGO=N).

Kosugi algorithm (special blocked-Davidson iteration scheme). This algorithm is the default in VASP.4.6 and VASP.5.X. It optimizes a subset of NSIM bands simultaneously. The optimized bands are kept orthogonal to all other bands. If problems are encountered with the algorithm, try to decrease NSIM. Such problems are encountered, if linear dependencies develop in the search space. By reducing NSIM the rank of the search space is decreased.

IALGO=44-48: Residual minimization method direct inversion in the iterative subspace (ALGO= F)

The RMM-DIIS algorithm reduces the number of orthonormalization steps (

O(N^3)

) considerably and is therefore much faster than IALGO=8 and IALGO=38, at least for large systems and for workstations with a small memory band width. For optimal performance, we recommend to use this switch together with LREAL=Auto). The algorithm works in a blocked mode in which several bands are optimized at the same time. This can improve the performance even further on systems with a low memory band width (default is presently NSIM=4).

The following sub-switches exist:

IALGO=44 steepest descent eigenvalue minimization
IALGO=46 residuum-minimization + preconditioning
IALGO=48 preconditioned residuum-minimization (ALGO=F)

Related Tags and Sections

LDIAG, LSUBROT

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