Linear Transit (LT)

One of the options in ADF is to scan a path on the energy surface. The path is defined by a systematic variation of one or more nuclear coordinates between user-specified initial and final values. The coordinates that are so varied are denoted the linear transit (LT) parameters. If there is more than one such parameter, all of them are varied simultaneously; the linear transit is therefore often called a synchronous linear transit. For each LT point on the scan, defined by a particular value of the path parameter(s), the remaining nuclear coordinates (or a subset of them), i.e., those that are not LT parameters, may be optimized. From a technical point of view, a LT run is simply a sequence of constrained optimizations.

One of the most useful applications of a LT is to get a reasonable estimate of a transition state. A classical example is the HCN to CNH transit, in which the hydrogen atom travels from one end of CN to the other. The LT parameter would here be the angle θ(H-C-N), changing from 180 degrees down to zero in 10 steps, say. For each particular θ-value, the HC and CN distances are optimized. By gathering the energy values at the LT points and interpolating them in a curve we obtain a fair view of the path, and hence, the location of the TS.

Links

ADF User Documentation: linear transit
ADF-GUI: structure and reactivity, Tutorial: HCN isomerization
Examples: reactivity
References: linear transit
Related: transition states