Hessian

GeoOpt%Hessian_cart

GeoOpt%Hessian inverted_cart

GeoOpt%Hessian_zmat

GeoOpt%Hessian inverted_zmat

All these four varieties are searched for if the new run searches for a restart Hessian matrix at all, that is: in an optimization, Linear Transit or Transition State search. As the names should suggest these variables stand for the Hessian, respectively the inverse of the Hessian in Cartesian or z-matrix coordinates.
In all cases the full square matrix must be present, with dimension the number of atomic coordinates, 3 times the number of atoms. This holds also for z-matrix coordinates. The 6 dummy coordinates play no role, the corresponding matrix elements in the Hessian should be zero.

If a Hessian is searched for on the restart file, all four possibilities above are tried and the first one found is used, the other ones being ignored. The order in which they are tried is:

If the current run uses Cartesian coordinates as optimization variables, then first the two cart varieties are tried, and vice versa for z-matrix optimization.

In a minimization (simple optimization or Linear Transit) first the inverted variety is tried; in a Transition State search the normal (not inverted) Hessian is looked for first.

Note: If a z-matrix Hessian is retrieved from the restart file the program will use the underlying z-matrix structure to derive a Cartesian Hessian from it. In such case the restart file must also contain:

GeoOpt%kmatrix

The z-matrix structure (references to the atoms in this matrix assume the ordering of atoms as used internally by the program).

Note: the kmatrix on the file need not be identical to the kmatrix used in the current calculation. In fact, the current calculation may not even have a z-matrix structure.