The Sparse keyword says to use sparse matrix storage for performance enhancement of large calculations (above around 400 atoms) [Daniels97]. The keyword's option allows you to specify the cutoff value for considering matrix elements to be zero.
See the Program Development-Related Keywords for options to this keyword.
Loose
Use loose cutoffs: 5.0-5
Medium
Use medium cutoffs: 5.0-7
Tight
Use tight cutoffs: 1.0-10
N
Set the cutoff to 10–N
None
Overrides the default of Sparse for ONIOM layers.
