ACE

References: Lin2016

Parameters for the Adaptively Compressed Exchange (ACE) operator. ACE replaces the full exchange matrix with a low-rank projector K_ACE = -W*W^T after an initial full HFX build, reducing cost of subsequent SCF steps. NOTE: ACE requires diagonalization-based SCF. It is incompatible with orbital transformation (OT) methods because OT does not construct MO coefficients. [Edit on GitHub]

Keywords

• ACTIVE

• REBUILD_FREQUENCY

Keyword descriptions

ACTIVE

Type: logical
Default: F
Lone keyword: T
Usage: ACTIVE .TRUE.

Description: Enable the ACE approximation for HFX. When .TRUE., the exchange matrix is replaced by the ACE projector after the first full build.

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REBUILD_FREQUENCY

Type: integer
Default: 20
Usage: REBUILD_FREQUENCY 20

Description: Rebuild the ACE projectors W every N SCF steps. N=1 means rebuild every step (identical to full HFX, use for testing only). N=10-20 is typical for production. Projectors are always rebuilt when the structure changes.

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