Basin constrained κ-dimer method for saddle point finding.

Area of Science:

• Chemical Physics
• Computational Chemistry
• Reaction Dynamics

Background:

• Transition state theory (TST) is crucial for calculating reaction rates.
• The dimer method is a common approach for locating saddle points in potential energy surfaces.
• Existing dimer methods can converge to irrelevant saddle points, complicating rate calculations.

Purpose of the Study:

• To address the issue of the dimer method converging to disconnected saddle points.
• To improve the accuracy and efficiency of finding relevant saddle points for escape rate calculations.
• To develop a modified dimer method that reliably identifies boundary saddle points.

Main Methods:

• Utilized the harmonic approximation to transition state theory.
• Employed the dimer minimum-mode following method for saddle point searches.
• Introduced a novel ridge definition based on minimum directional curvature (κ) of isopotential hyperplanes.
• Constrained dimer dynamics within the κ < 0 region.

Main Results:

• Demonstrated that standard dimer searches can yield disconnected saddles, not on the reactant boundary.
• Showed that local ridges tracked by the dimer method deviate from true ridges.
• Found that hyperplanes with κ = 0 pass through all saddle points.
• Confirmed that restraining the dimer to κ < 0 significantly reduces convergence to disconnected saddles.

Conclusions:

• The modified dimer method effectively enhances the probability of finding connected saddles.
• This approach improves the reliability of calculating chemical reaction escape rates.
• The use of minimum directional curvature offers a robust strategy for navigating potential energy surfaces.