If LSCALAPACK= .FALSE. scaLAPACK will not be used by VASP.
This switch is required on the T3D/T3E if VASP was compiled with the scaLAPACK and several images are run at the same time by setting IMAGES=X in the INCAR file (see next section). If scaLAPACK is not switched of in the nudged elastic band mode on the T3D/T3E, VASP will crash.
In some cases, the LU decomposition (timing ORTHCH) based on scaLAPACK is slower than the serial LU decomposition. Hence it also is possible, to switch of the parallel LU decomposition by specifying LSCALU=.FALSE. in the INCAR file (the subspace rotation is still done with scaLAPACK in this case).
MIND: in the Gamma point only T3D version, the parallel sub space diagonalisation (LscaLAPACK=.TRUE.) is performed with a Jacobi algorithm instead of scaLAPACK. This routine was written by Ian Bush. The Jacobi routine is faster than scaLAPACK.