LDIAG

LDIAG = [logical]
Default: LDIAG = .TRUE.

Description: This tag determines whether a subspace diagonalization is performed or not within the main algorithm selected by IALGO.

For ALGO=Normal, Fast, and Very Fast, VASP performs a diagonalization in the subspace spanned by all orbitals. This is often referred to as Rayleigh–Ritz method. The step increases the convergence rate and thus is expedient in most cases. For the algorithms that optimize

https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Ritz_method