Numerical differentiation : **NMDDRV

This module can calculate any geometrical derivative of the energy using either as high analytical derivatives as possible, or using the specified level of analytical derivatives (assuming implemented for the choice of wave function) [113]. Also performs vibrational averaging over selected first- and second-order molecular properties.

.DISPLACEMENT

READ (LUCMD,*) DISPLC

Reads in the step lengths (in atomic units) that is to be used in the numerical differentiation scheme. Default is 1.0D-2.

.DORDR

READ (LUCMD,*) NMORDR, NAORDR

Sets the numerical (NMORDR) and analytical (NAORDR) differentiating order for calculating force constants. Current implementation has an artificial boundary at the 5. numerical derivative (independent of the analytical differentiation order). Notice that if you would like to calculating 4.derivatives from analytical 2.derivatives the input would be 2 2, since you would like to get 2.order numerical derivatives from 2.order analytical derivatives.

.DRYRUN

READ (LUCMD,*) NMREDU
READ (LUCMD,*) (KDRYRN(II),II=1,NMREDU)

The numerical derivatives will not be calculated, and the program will just set up the required displacement. An optional number of redundant coordinate displacements can be specified, corresponding to translational and rotational degrees of freedom.

.HARMONIC FORCE FIELD

At the end of the calculation, perform a vibrational analysis using the calculated Hessian matrix.

.MANUAL

Dump each individual geometry input file to the DALTON.OUT file. Primarily of interest for debugging purposes.

.NORMAL

Using this keyword the numerical differentiation will be carried out with respect to normal coordinates. The program will then do the necessary numerical differentiation to get the Hessian (and thus normal coordinates), before it will carry on calculating the higher-order force field requested with respect to the calculated normal coordinates.

.PRECALCULATED HESSIAN

Use a precalculated Hessian available on the DALTON.HES file when defining normal coordinates. Only active in combination with the keyword .NORMAL.

.PRINT

READ (LUCMD,*) IDRPRI

Control the print level in the numerical derivative routines. Default is the same as the general print level IPRUSR.

.PROPAV

Indicates that a averaging over vibrational motions of a molecular property (including the energy) is to be performed. The input for what kind of a vibrational analysis is to be performed is specified in the *PROPAV module.

.PROPER

READ (LUCMD,*) NMRDRP, NARDRP

Sets the numerical (NMRDRP) and analytical (NARDRP) differentiating order for calculating geometrical derivatives of molecular properties. Currently, the possible presence of analytical property derivatives cannot be taken advantage of, and the default value of $0$ for NARDRP should be used. Currently, dipole transition strengths and vibrationally averaged spin-spin coupling constants have been implemented, the former also for Coupled-Cluster wave functions. Notice that vibrationally averaged spin-spin coupling constants also can be calculated using the .VIBANA and *VIBANA keywords and input section.

.RESTRT

Controls the restart procedure. If a calculation crashes during a force constant calculation, there will be a file in the work directory called RSTRT.FC. This will contain all of the information necessary to restart the calculation. If this file is available and the keyword is used, DALTON will attempt to restart the calculation.

.REUSE HESSIAN

If a (mixed) numerical Hessian has been calculated, it will be saved in the file DALTON.HES for possible future use.

.SDRTST

If analytical Hessian also has been requested and second-order numerical derivatives, a comparison of the numerical and analytical Hessian will be done. Primarily used for testing.

.SPECTRO INTERFACE

Write an interface file DALTON.SPC containing force fields of different orders suited for analysis with the SPECTRO program [].

.SYMMET

READ (LUCMD,*) FCLASS

Assigns the molecular point group of the molecule (FCLASS). For instance for water FCLASS would be equal to ``C2v''. Main rotational axis needs to be set to the z-axis in the .mol file. Additional generating elements needs to be the x-axis for a C2 rotation, and the xy plane for a mirror plane. The current implementation only allows for symmetry use, when differentiating from energies.

.TEST N

Test if the normal coordinates used for calculated geometrical derivatives give rise to force fields with appropriate symmetries. Mainly for debugging purposes.