Frequencies

In the continuation of a Frequencies calculation all Frequencies-related data are retrieved from the section Freq on the restart file. (SCF fit data are, as always, retrieved from the section Fit). A fairly large number of items will be read and must all be present (if a section Freq is present in a restart file supplied to a Frequencies run). Technical parameters such as the type of numerical differentiation, size of displacements etc. are read from the restart file. Any input specifications are ignored.

Freq%kountf

Counter of number of geometries completed. In a non-restart run this is initialized at zero; in a restart it is read from the file.

Freq%nraman

Flag for RAMAN calculations

Freq%numdif

1 or 2: defines numerical differentiation used to compute the force constants from the gradients in slightly displaced geometries (by 1-point or 2-point differentiation).

Freq%disrad

Size of displacement for cartesian or bond-length displacements.

Freq%disang

Size of angular (bond angle, dihedral angle) displacements.

Freq%atmcrd

zmat or cart: specifies whether a z-matrix structure is present. This does not define the type of displacement coordinates, see the next item.

Freq%geocrd

Type of coordinates in which the displacements are carried out: zmat or cart

Freq%nfree

Number of free and independent displacement variables.

Freq%idfree

References from the atomic coordinates (in internal order) to the independent displacement variables.

Freq%all freedoms

(logical) flags whether or not the complete energy surface is scanned around the equilibrium or only part of the internal degrees of freedom are used.

Freq%xyz

equilibrium coordinates (internal order of atoms).

Freq%kmatrix

Z-matrix structure. Pointers are indexed by and refer to atoms in the internally used order.

Freq%zmatrix

Z-matrix coordinates of the equilibrium geometry (internal ordering of atoms).

Freq%rigids

6 rigid motion vectors (one may be zero, in case of a linear molecule). Each vector has as many components as there are atomic coordinates. The values correspond to the internal ordering of atoms.

Freq%xyz displaced

Cartesian coordinates of displaced geometry to carry out now. In a non-restart run this would be the equilibrium geometry.

Freq%zmatrix displaced

Similar for the Z-matrix coordinates.

Freq%Dipole previous

dipole vector (3 components) for the last geometry handled.

Freq%Dipole

dipole at the equilibrium geometry.

Freq%Dipole derivatives

Derivatives of the dipole wrt atomic coordinate displacements.

Freq%Gradients previous

Energy gradients (derivatives wrt atomic coordinate displacements) in the last handled geometry.

Freq%Force constants

Matrix of force constants. This is, together with the Dipole derivatives the final quantity to compute. At each cycle of the Frequencies data are added to it. Upon completion of the Frequencies cycles the frequencies and normal modes are computed from it. Together with the dipole derivatives it then also yields the InfraRed intensities.