How to Use PESPointCharacterization: Fast Transition State Verification
Part 7 of our AMS Weekly Video Series
In this week’s video, Matti Helmström demonstrates how to efficiently verify transition state (TS) searches in the Amsterdam Modeling Suite using the PESPointCharacterization feature of the AMS driver.
Transition state verification is a crucial step in reaction mechanism studies—ensuring that an optimized geometry truly represents a first-order saddle point with exactly one imaginary frequency. In this example, a Claisen rearrangement is used as the model reaction. The workflow begins with a DFTB-optimized TS and proceeds to refine it with ADF using the R2SCAN-3C functional, a robust, non-hybrid DFT approach implemented with Slater-type orbitals.
A key focus of the video is the comparison between two methods for confirming TS character:
- Full vibrational analysis, which computes all normal modes but requires substantial computational effort
- PESPointCharacterization, which extracts only the lowest vibrational modes needed to confirm the presence of the single imaginary frequency
Both methods lead to the same verified transition state, but PESPointCharacterization dramatically reduces the calculation time—often to just a fraction of the full normal-mode computation. By avoiding unnecessary vibrational modes, users can accelerate TS workflows without compromising reliability.
The video also highlights best practices for transition state optimization, such as providing an approximate initial Hessian (e.g., via DFTB) to improve convergence and stability. While PESPointCharacterization is ideal for quick TS verification, full frequency calculations remain essential when free energies or thermodynamic corrections are required.
This streamlined approach helps researchers perform faster, more targeted TS analyses, enabling efficient exploration of reaction pathways and mechanistic insights across chemistry and materials modeling.
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