Structure and Reactivity
Geometry optimizations, transition states, and reaction paths
ADF enables geometry optimizations in delocalized, Cartesian, and internal coordinates. An initial Hessian estimate speeds up the optimizations. Various constraints (including initially unsatisfied and combined) can be imposed. Transition state (TS) searches (via Eigenvector Following methods and Nudged Elastic Band (NEB)), intrinsic reaction coordinates (IRC), and linear transit (LT) calculations are available to further analyze the energy path from reactants, via the transition state, to the final products. The new analytic second derivatives implementation rapidly yields Hessians for GGA functionals, which are helpful in finding and characterizing the transition states.
- geometry optimizations
- linear transit (LT)
- transition state (TS) searches, NEB
- intrinsic reaction coordinates (IRC)
ADF also enables a transparent description and a detailed understanding of activation barriers and relative efficiencies of competing reaction mechanisms, and how they may be affected by modifying the reactants or reaction conditions (e.g. solvation). For example, in the activation strain model (ATS) the activation energy is decomposed in the energy necessary to deform the separate reactants to the geometry they adopt in the activated complex and the interaction energy between the deformed reactants in the transition state. A key concept in this model is the fragment approach available in ADF.
Links
ADF User Documentation: geometry optimization,
LT,
TS,
NEB,
IRC,
second derivatives
ADF-GUI: structure and reactivity,
Tutorial:
geometry optimization,
reactivity,
tutorial structure building
Examples: geometry optimization,
reactivity
References: TS,
NEB,
IRC
Related: fragment approach, bond energy analysis
