Global Reaction Route Mapping

GRRM

Explore potential-energy surfaces with ADDF and AFIR-family methods, then validate and refine equilibrium structures, transition states, and dissociation channels.

Role: Automated reaction-path exploration
Typical input: Initial geometry and calculation engine
Typical output: EQ, TS, DC, reaction network

1. Potential-energy-surface exploration

GRRM searches stationary points and connecting paths rather than optimizing only a user-supplied guess. Labels such as EQ, TS, and DC describe equilibrium structures, transition states, and dissociation channels.

Search completeness depends on the starting structures, search options, energy ceiling, collision-energy parameters, and termination conditions. A generated network is therefore a model of the explored region, not proof that every pathway has been found.

2. Gaussian and xTB engines

The search algorithm and energy/gradient engine are separate choices. xTB enables broad low-cost exploration; selected structures and paths can then be refined with Gaussian or another higher-level engine.

Use one consistent low-cost level during broad exploration. Re-evaluate selected structures and pathways at a common higher level rather than mixing raw energies from different engines.

# Conceptual workflow; use the syntax for the installed GRRM release.
grrm search-input.com
# Refine selected EQ/TS structures with the chosen Gaussian or xTB engine.

3. Potential-energy surfaces and GRRM output

Label	Meaning	Required check
EQ	Equilibrium structure	No significant imaginary frequency
TS	First-order saddle point	One relevant imaginary mode and connected endpoints
DC	Dissociation channel	Fragments, charge, spin, and asymptotic behavior

4. ADDF

Anharmonic downward distortion following uses local anharmonic directions around a minimum to discover dissociation pathways systematically. Cost grows rapidly with molecular flexibility.

ADDF follows anharmonic downward distortion directions from an equilibrium structure. The number of directions and computational cost grow rapidly with molecular size and flexibility.

5. AFIR concept

AFIR introduces an artificial force between fragments or atom groups to lower barriers during exploration. Candidate paths must subsequently be reoptimized on the unmodified potential-energy surface.

Artificial-force paths require refinement

Energies along an AFIR path contain the artificial-force bias. Remove the force, optimize the candidate TS and minima, and validate their connection on the original potential-energy surface.

6. SC-AFIR

Single-component AFIR explores transformations within one connected system and is useful for intramolecular rearrangements. Fragment definitions and collision-energy parameters control search scope.

7. MC-AFIR

Multi-component AFIR is designed for association and reactions among multiple components. Initial orientations, fragment choices, and duplicate-path treatment are central to coverage.

8. Validation and refinement

Inspect structures and connectivity.
Refine selected EQ and TS structures consistently.
Verify frequencies and transition vectors.
Confirm endpoints by IRC or path following.
Recalculate energies and thermal corrections at the final level.

9. References

Last reviewed: August 4, 2026. Check the linked official documentation for syntax specific to the installed software version.