Name
NOHL — Avoid computation of the HOMO-LUMO orbitals and gap.
Description
Certain properties, such as the ionization potential, the homo-lumo gap, and optionally the hyperfine
coupling constants (HYPER) are generally
computed automatically using the molecular orbitals and energy level information generated during
the SCF procedure. The new PSOLVE
methods (or SPARSE which implies it) solve
for the density matrix directly and so does not produce this molecular orbital information. To get arond this
limitation, a special routine is used to solve for a small subset of canonical molecular orbitals
surrounding the molecule's HOMO-LUMO gap using a Davidson diagonalization scheme. This
is also needed for SCFLOCAL, which
produces localized molecular orbitals rather than the canonical ones. While this solver is generally
fast and reliable, it does still require a noticable amount of CPU time and so can be supressed by
the NOHL keyword.
