This keyword activates the frequency analysis.
FIXED || A partial frequency analysis is requested. |
RAMAN || The Raman intensities are calculated. |
RESTART || The frequency analysis is restarted from the
deMon.rst file. |
VIB=Real || Scaling factor for the numerical step size.|
By default, the infra-red intensities of the vibrations are calculated. With
the option RAMAN, the Raman intensities (in atomic units) and the depolarization
ratio  are calculated also. This is considerably more time-consuming
than a standard frequency analysis. The RESTART option permits the
restart of a frequency analysis. The Hessian matrix elements already calculated
are read from the restart file deMon.rst and the analysis is continued.
The numerical step size can be scaled with the VIB option. By default, the step
size is 0.005 a.u. for all theoretical models. With VIB=2 or VIB=0.2, this step
size can be scaled to 0.01 a.u. or 0.001 a.u., respectively. Note that numerical
frequency calculations can be sensitive to the SCF convergence. To improve the SCF
convergence in the finite-step SCF calculations the options TOL and CDF of the
SCFTYPE keyword (see 4.5.1) can be used.
The FIXED option specifies a partial frequency analysis, that is, calculation
of frequencies involving only the motion of certain atoms. The element
or atomic symbols of the atoms that are to be treated in the frequency analysis
must be specified in the keyword body of the FREQUENCY keyword. The
following example input shows a frequency analysis for the CO in
the CuCO cation.
GEOMETRY Z-MATRIX ANGSTROM
C Cu R1
O C R2 Cu 180.0
The calculated CO stretching frequency of 2250 cm is in excellent
agreement with the result from an unconstrained frequency analysis