Quick Reaction Coordinate

A quick reaction coordinate job maps reactant and product endpoints from a transition-state guess by displacing along the imaginary-frequency normal mode and optimizing to the nearest minima.

This method is a fast alternative to full IRC path following — instead of tracing the reaction path step-by-step, it displaces the TS geometry in both directions and performs two geometry optimizations.

What It Runs

For each submitted job, Atomiverse executes:

1. Saddle-point optimization on the TS guess.
2. Vibrational analysis on the optimized structure.
3. Validation that exactly one imaginary frequency exists (the reaction coordinate mode).
4. Displacement along the reaction mode in both forward and reverse directions.
5. Geometry optimization of each displaced structure to a minimum.

The result is the TS, reactant, and product structures, together with forward and reverse reaction barriers.

Your First Quick Reaction Coordinate

import atomiverse
from atomiverse import (
    Atoms,
    JobFailedError,
    QuickReactionCoordinate,
)
from atomiverse.levels import GFN2_XTB

atomiverse.configure(api_key="your-api-key")

ts_guess = Atoms.from_smiles("[H][H]")

job = QuickReactionCoordinate(
    ts_atoms=ts_guess,
    level_of_theory=GFN2_XTB,
)
job.submit()

try:
    result = job.require_result()
except JobFailedError as exc:
    print(f"Job failed: {exc.failure.error}")
else:
    print(f"TS Energy:      {result.ts_energy:.6f} eV")
    print(f"Forward barrier:  {result.barrier_forward:.3f} eV")
    print(f"Reverse barrier:  {result.barrier_reverse:.3f} eV")
    print(f"Reaction energy:  {result.reaction_energy:.3f} eV")

Input Parameters

Required:

• ts_atoms: transition-state guess structure
• level_of_theory: electronic-structure method

Optional:

• charge (default 0)
• multiplicity (default 1)
• amplitude (default 0.3): scaling factor for displacement along the reaction coordinate. Larger values push further from the saddle point; smaller values are safer for crowded geometries.

job = QuickReactionCoordinate(
    ts_atoms=ts_guess,
    charge=0,
    multiplicity=1,
    level_of_theory=GFN2_XTB,
    amplitude=0.4,
)

Result

job.require_result() returns a QuickReactionCoordinateResult.

Field	Type	Description
ts_atoms	Atoms	Optimized transition-state structure.
reactant_atoms	Atoms | None	Optimized reactant endpoint.
product_atoms	Atoms | None	Optimized product endpoint.
ts_energy	float	TS energy in eV.
reactant_energy	float | None	Reactant energy in eV.
product_energy	float | None	Product energy in eV.
barrier_forward	float | None	Forward barrier (TS − reactant) in eV.
barrier_reverse	float | None	Reverse barrier (TS − product) in eV.
reaction_energy	float | None	Reaction energy (product − reactant) in eV.
imaginary_frequency_cm1	float | None	Reaction mode frequency in cm⁻¹.
ts_optimization_trajectory	list[TrajectoryStep]	Steps of the saddle-point search.
forward_converged	bool	Whether forward optimization converged.
reverse_converged	bool	Whether reverse optimization converged.

Non-blocking Submission

from atomiverse import State

job.submit(wait=False)
job.refresh()

if job.state == State.DONE:
    result = job.require_result()
    print(f"Forward barrier: {result.barrier_forward:.3f} eV")
elif job.state == State.FAILED:
    print(job.require_failure().error)