Analysis Keywords

These keywords request population analyses, resonance structure probabilities, and structure searches beyond the standard EDF.

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PRSRS n1 n2 … nG

Compute the probability of finding exactly n1 electrons in group 1, n2 in group 2, …, nG in group G — a specific Real-Space Resonance Structure (RSRS).

Multiple PRSRS lines may appear in the input to request several structures at once.

Example — probability of the (2,2,2) configuration in a 3-group molecule:

PRSRS 2 2 2

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MAXPOP m1 m2 … mG

When computing PRSRS, restrict the spin-resolved search to configurations where group i has at most mi alpha or beta electrons. Must appear after a PRSRS line.

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MINPOP m1 m2 … mG

When computing PRSRS, restrict the spin-resolved search to configurations where group i has at least mi alpha or beta electrons. Must appear after a PRSRS line.

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TWOCENDI [epsbond]

Compute all two-center delocalization indices \(\delta(A,B)\) between every pair of atoms. epsbond is a threshold: atoms A and B are reported as bonded if \(\delta(A,B) > \text{epsbond}\). Default is 1.0.

The calculation is run ten times with thresholds epsbond, epsbond/2, …, epsbond/2⁹.

Warning

Only works with single-determinant wavefunctions. Not available for CASSCF.

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OQSEOS

Perform an Open Quantum System Effective Oxidation State (OQS-EOS) analysis of each fragment and stop. Computes the EOS of each fragment from the 1-RDM of the open system.

Requires a prior alpha and beta 1-RDM computation. Only closed-shell coupled-cluster wavefunctions are supported for CCWFN inputs; CASSCF wavefunctions are also supported.

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OQSLEWIS

Search for Lewis structures based on the user-defined fragments using the OQS approach. Control passes to lewisoqs.f, and edf stops after the search.

Use NFRAG to define a fragment count different from NGROUP for the Lewis search.

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FNO atom1 atom2 …

Compute the Fragment Natural Orbitals (FNOs) for the fragment formed by atoms atom1, atom2, …. Multiple FNO lines may appear. After all FNO computations, edf stops.

FNOs are the natural orbitals of the reduced density matrix of the fragment, obtained by diagonalizing the fragment's one-body density matrix within the AOM framework.

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DIRPROB

Compute probabilities by a direct brute-force enumeration over all real-space resonance structures whose electron counts fall within [minpopul(i), maxpopul(i)] for each fragment. Stopping criterion after all structures are found.

Warning

Only works for single-determinant wavefunctions. Scales exponentially with molecule size — use only for small systems with few fragments.

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DOENTROPY

Compute the Mutual Information Entropy (MEI) after the EDF is computed. MEI quantifies the total electron correlation between the defined fragments.

Default is to skip this — MEI output can be very large for many fragments. See also Output Control — DOENTROPY.

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BONDING … ENDBONDING

Fit the molecular EDF to a model composed of 2-center-2-electron (2c,2e) bonds and optionally 3-center-2-electron (3c,2e) bonds. The block ends with ENDBONDING.

This fitting minimizes a weighted objective:

\[\Delta = W_\text{EDF} \cdot A + W_\text{POP} \cdot B + W_\text{DIS} \cdot C\]

where \(A\) is the mean squared difference between model and exact probabilities, \(B\) is the population error, and \(C\) is the delocalization-index error.

Keywords within the block:

Keyword	Syntax	Meaning
ENDBONDING	—	End the block (mandatory)
TYPE	type qq ifixq ffty ifixf	Define a 2c,2e bond type
TYPE3C	type p200 p020 p002 p110 p101 f200 f020 f002 f110 f101	Define a 3c,2e bond type
PAIR	frag1 frag2 type [rtype]	Place a 2c,2e bond between fragments
TRIO	frag1 frag2 frag3 type [rtype]	Place a 3c,2e bond between fragments
EPSBOND	real	Convergence threshold (default 1e-4)
INICVAR	real	Initial step parameter (default 0.1)
PRIN	int	Print level (default 0)
WEDF	real	Weight of EDF term (default 1.0)
WPOP	real	Weight of population term (default 0.0)
WDIS	real	Weight of DI term (default 0.0)

For TYPE: qq is the bond polarity (optimized if ifixq ≠ 0); ffty is the correlation factor (optimized if ifixf ≠ 0). Default starting values of qq = 0.5, ffty = 0.0 are typical.

Example — two H–H bond types, one bond:

BONDING
  TYPE  1  0.5  1  0.0  1
  PAIR  1  2  1
ENDBONDING