[symmetry]

The [symmetry] section controls point-group metadata, the guarded abelian integral reduction, and optional experimental symmetry tiers. Labeling can be useful even when reductions are disabled.

Detection is on by default

enabled defaults to true. Detection and labeling are active unless you turn them off. The two reduction keywords — use_integral_symmetry and use_response_symmetry — remain False by default, so the geometry is not reoriented, the full integral list is still used, and reference-SCF or ordinary HF/DFT ground-state energies are unchanged. An MRSF physical S0 remains a response root and can change when symmetry information repairs response-block coverage.

Detection is not purely cosmetic, though. The detected irreps are what let the excited-state solver reach every symmetry block, so excited-state results can differ from a run with detection off — and where they do, the difference is a correction. See Molecular symmetry.

Keywords

enabled

Field	Value
Type	string
Default	true
Values	false, true, auto
Used by	symmetry detection

Controls symmetry detection. When on, OpenQP detects the point group and its Abelian subgroup, labels orbitals, states and normal modes, and makes the per-pair irrep table available to the excited-state solver.

What it does not do: it does not reorient the molecule and does not reduce the integral list. Those follow use_integral_symmetry only.

Set enabled=false to restore the pre-detection behavior — no labels, no irrep table, and the excited-state trial vectors chosen purely by orbital-energy gap (see Molecular symmetry for why that can matter).

point_group

Field	Value
Type	string
Default	auto
Used by	requested point group

Requested point group, or auto for automatic detection.

subgroup

Field	Value
Type	string
Default	auto
Used by	Abelian subgroup selection

Requested Abelian subgroup, or auto for automatic choice.

label_mo

Field	Value
Type	boolean
Default	True
Used by	MO labeling

Prints the molecular-orbital symmetry table. This is a display control only: setting it to False suppresses the printed table but does not disable the orbital irreps themselves, which the excited-state solver needs regardless.

label_states

Field	Value
Type	boolean
Default	True
Used by	response-state labeling

Labels excited states by symmetry where possible. When [tdhf] multiplicity is set, the labels are reported as spin-resolved terms (1A1, 3B2, ...) rather than bare irreps.

label_modes

Field	Value
Type	boolean
Default	True
Used by	vibrational-mode labeling

Labels vibrational modes by symmetry where possible. The labels appear as a Symmetry column in the printed frequency table:

   Mode  Symmetry     Frequency(cm-1)      IR(km/mol)        Raman(activity)
      1        a1           2043.11         0.492662           104.268372
      2        a1           4488.55         1.622292           558.762685
      3        b2           4790.80         0.866146           220.085777

The column is present whenever mode labels could be assigned, including for a Hessian restored with [hess] read=true.

use_integral_symmetry

Field	Value
Type	string/boolean-like
Default	True
Used by	integral symmetry reduction

Enables the guarded abelian petite-list/skeleton-Fock reduction for supported energy and grad calculations. The default route verifies the AO operator against the overlap matrix, verifies density invariance before each reduced build, and falls back to the complete integral path when a safety condition is not met. ROHF calculations using pFON also stay on the complete C1 integral path because fractional-occupation convergence can be sensitive to the changed summation order. Set this to False to disable integral reduction. The value full requests the experimental non-abelian tier and should be validated against a C1 reference run.

move_to_standard_frame

Field	Value
Type	boolean
Default	False
Used by	integral symmetry reduction

Controls whether a calculation with use_integral_symmetry=true is rotated and translated to a standard symmetry frame before the integral reduction is staged. The default False keeps the molecule in its input frame; OpenQP then uses the corresponding input-frame symmetry operators for the integral and gradient reductions. The no-move route is available for energy and grad calculations and uses the abelian integral-symmetry tier. The non-abelian use_integral_symmetry=full tier requires move_to_standard_frame=true; OpenQP rejects full together with move_to_standard_frame=false instead of silently using a smaller group. As with every integral-symmetry calculation, validate new systems against a run with use_integral_symmetry=false.

[symmetry]
enabled=true
use_integral_symmetry=true
move_to_standard_frame=false

This is the keyword that reorients the molecule into the symmetry standard orientation. Turning symmetry detection on does not.

Accepts true for the Abelian subgroup (machine-exact) or full for the complete point group (a larger reduction, accurate to roughly 1e-7).

full is declined for DFT

The full tier reduces the two-electron integrals over the complete point group, while the exchange-correlation grid necessarily stays on the Abelian operations — Lebedev angular grids are not invariant under C3/C6 rotations. The two halves would then reduce over different groups, which is a measured error of about 3e-04 Hartree.

When a functional is set, OpenQP therefore falls back to the exact Abelian tier and says so in the symmetry log block. You still get the reduction, just the tier that is exact. Remove the [input] functional if you need the full group — OpenQP selects DFT with method=hf plus a functional, so method=hf alone is not what distinguishes the two.

The fallback is never silent: if the reduction is requested but does not engage for any reason, the log states that the run used the full (C1) integral list.

Accepted values are false, true and full. true selects the Abelian subgroup; full requests the complete point group.

What the reduction covers

Enabling this keyword reduces two separate parts of the calculation:

• The two-electron integral list. Symmetry-equivalent shell quartets are computed once and reweighted, and the resulting skeleton Fock matrix is projected back.
• The exchange–correlation quadrature. Grid slices belonging to symmetry-equivalent atoms are computed for one representative atom per orbit and scaled by the size of that orbit; the images are skipped.

The XC reduction engages only when the molecule actually has an orbit to exploit — that is, when at least one atom is a symmetry image of another. For a C1 molecule, or a geometry in which every atom sits on a special position, every atom is its own orbit, so nothing is skipped and the reduction reports itself inactive rather than doing identity work.

The XC reduction is not compatible with the cross-iteration Φ cache. When it engages, [scf] xc_phi_cache is disabled automatically for that run: a cached grid block built under the reduction would otherwise be replayed unreduced and give a silently wrong E_xc.

Geometry and run types

Enabling the reduction reorients the molecule into the symmetry standard orientation, and all outputs — geometry, gradients, orbitals — are reported in that frame.

The reduction is applied only to runtype = energy and runtype = grad. Other run types (optimisation, numerical Hessian, NEB, MEP, properties) are excluded, because they either displace the geometry themselves or consume an externally supplied one, and a per-step frame change would be assembled inconsistently.

full with a functional

use_integral_symmetry = full is declined for any run that sets [input] functional, and the exact Abelian tier is used instead. The two halves of the Fock matrix would otherwise reduce over different groups: Lebedev angular grids are invariant under the axis-aligned octahedral operations but not under C3 or C6, so the XC half can only ever be Abelian-symmetric while the JK half would be forced symmetric under the full group. The mismatch is a measured error rather than a rounding difference. The log states when this fallback happens; it is not silent.

Hartree–Fock runs are unaffected and may use full.

use_response_symmetry

Field	Value
Type	boolean
Default	False
Used by	response solver symmetry reduction

Enables irrep-blocked response updates — the experimental projection that confines Davidson residuals to a single irrep. The checker marks this as experimental and recommends validating excitation energies against an unblocked run.

This is separate from the symmetry-block coverage of the initial trial vectors, which is not experimental and follows detection alone. The symmetry log block distinguishes the two:

response blocking	Meaning
pair_table_staged	Irrep table built for trial-vector coverage; the residual projection is off
active	The experimental residual projection is running

tolerance

Field	Value
Type	float
Default	1.0e-5
Used by	symmetry detection

Geometry tolerance for symmetry detection. Must be positive.

strict

Field	Value
Type	boolean
Default	False
Used by	requested/detected group matching

Requires stricter agreement between requested and detected symmetry labels.