In a continued Intrinsic Reaction Coordinate (IRC) calculation, the continuation run processes the path(s) as specified in input. Any info for such path(s) on the restart file will then be used to continue from there. If the restart file contains the relevant IRC sections, see below, then all relevant data must be present on it and correct (i.e. matching those of the current run.
The sections on file pertaining to the IRC are:
IRC: this section contains information about the central (TS) point, which variables are optimized in each of the IRC points, the connection matrix defining the z-matrix structure, etc.
IRC_Forward and IRC_Backward: these sections contain the data of the two paths from the Transition State down to the two adjacent local energy minima: for each point the distance from the previous point and the local curvature and molecular properties such as energy, atomic charges and dipole moment.
LT%nr of points
The number of points by which the LT is scanned; this is identical to the Fortran variable ltimax in the code. The value on the restart file applies in the calculations and overwrites any input/default value (see the subkey lineartransit of the geometry block)
LT%current point
Index of the current LT scan point. This is where the program will continue. In a non-restart LT run, this index initializes at 1.
lt%Energies
An array with energy values, one for each LT point. When the LT run is completed, this array allows you to map out the energy along the LT path. The values for the completed LT points are stored on the restart file. This size of the array on the restart file must (at least) be the total nr of points on the complete path.
lt%Parameters
Initial and final values for the LT parameters, which describe roughly the path (all other coordinates may be optimized at each point, depending on other input keys). The values from the restart file overwrite input values. The input values should be supplied, however, as if it were a non-restart run.
lt%atmcrd
zmat if a z-matrix structure is available for the molecule, cart otherwise. This is used to control printing of results. It does not define the type of optimization variables: see the next item.
lt%geocrd
zmat or cart: the type of optimization variables. This defines in which type of coordinates the LT parameters are defined and any optimization of other coordinates takes place.
lt%xyz
Cartesian coordinates for all LT points: 3*atoms*ltpoints. The size of the array must conform to this. Only the values of the completed LT points and those of the current point are relevant. Those of the current LT point are used as initial coordinates to start the current run.
LT%zmatrix
Same for the Z-matrix coordinates. They should match the Cartesian coordinates for the completed LT points (this is not checked). Those for the current LT point will be recomputed from the current Cartesian coordinates.
