Keyword category:

Transition State Location

PATH=n.n

Description

This option follows a weighted steepest descent path in internal coordinates. (A more detailed description of the PATH algorithm can be found in Chapter 4, Computational Procedures.) Keyword T.V. or T.V.=n can be used to specify the initial direction and WEIGHT can be used to weight the coordinate system. The most common application is to begin at a transition state geometry and move in the direction of the transition vector. Geometries and properties will be reported at regular intervals along the path. When PATH is specified alone, the default spacing between reported points is chosen based on the total number of degrees of freedom, N, of the system (default spacing = min(0.08*sqrt(N),1.5) Angs). Use PATH=n.n to set this spacing between these reported points to n.n Angstroms.

IRC differs from PATH in that it runs weighted Cartesian coordinates rather than internal coordinates. Since PATH runs in internal coordinates, it can utilize symmetry constraints, whereas IRC can not. IRC also relies on computing second derivatives and so is more reliable but also more expensive then PATH. Because IRC (unlike PATH) uses the Hessian, IR frequencies and THERMO properties can be computed at each point along the IRC.

See also:

T.V., WEIGHT, IRC.