SPARSE — Perform sparse matrix calculation using the specified neglect threshold.

SPARSE=TIGHT

SPARSE=MEDIUM

SPARSE=LOOSE

SPARSE=`n.nnn`

This keyword turns on a sparse matrix calculation (otherwise the equivalent full matrix calculation is performed). If a PSOLVE method is not specified, then by default the purification of the density matrix (PDM) method will be used.

Perform a sparse matrix calculation neglecting matrix elements smaller than
1 × 10^{-8}. The resulting energy should reproduce the equivalent
full matrix result to within nano-hartree accuracy.

Perform a sparse matrix calculation neglecting matrix elements smaller than
1 × 10^{-6}. The resulting energy should reproduce the equivalent
full matrix result to within micro-hartree accuracy.

Perform a sparse matrix calculation neglecting matrix elements smaller than
1 × 10^{-5}. The resulting energy should reproduce the equivalent
full matrix result to within milli-hartree accuracy.

`n.nnn`

Perform a sparse matrix calculation neglecting matrix elements smaller than
* n.nnn*. A larger value will eliminate more values thus saving
CPU time and lowering memory and disk space requirements but will correspondingly increase
the error in the overall calculation. A value much larger than 1 × 10

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