CASTEP > Tasks in CASTEP > Setting up CASTEP calculations > Setting up a transition state calculation

Setting up a transition state calculation

CASTEP transition-state searches are performed using synchronous transit methods. These work best in situations where the structures of the reactants and products are known, but the location of the transition state is not.

A transition-state search requires a trajectory document (for example, an .arc or .xtd file) as input. The reactants are taken from the first frame of the trajectory, and the products from the last frame. For quadratic synchronous transit (QST) calculations, the current frame is used for the QST mid-point. The trajectory files generated by any of the other transition state search methods may be used as input to a QST run.

When a transition state search is performed on a periodic system the unit cell is fixed.

For a detailed description of the quality settings please refer to the Setting the quality of a calculation topic.

Synchronous transit calculations are performed in Cartesian coordinates. There is no option to override this.

To set up a synchronous transit calculation

  1. Begin by constructing two separate documents, one for the reactants and a second for the products.
  2. Determine the correspondence between atoms in the two documents using the Find Equivalent Atoms tool. The synchronous transit method performs a geometric interpolation between the atomic coordinates of the atoms in the reactants and the atoms in the products. In order to accomplish this, it is necessary that the program understand which atom matches to which.
  3. Generate a trajectory that converts reactants into products using the Reaction Preview tool. You can animate this document to check that the reactants are converted correctly to products. If you are satisfied with the match, proceed with the calculation. If not, use the Find Equivalent Atoms tool to edit the atom correspondence and try again.
  4. Using the document that was created by the Reaction Preview tool, select your options for the TS Search calculation and submit the CASTEP calculation by clicking the Run button.

To optimize the reactant and product structures as part of the TS Search run, check the Optimize reactants and products checkbox on the CASTEP Transition State Search dialog.

See Also:

Synchronous transit methods
Finding equivalent atoms
Previewing reaction pathways
CASTEP Transition State Search task
CASTEP Transition State Search dialog

Accelrys Materials Studio 8.0 Help: Wednesday, December 17, 2014
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