MOLPRO

43 VIBRATIONAL FREQUENCIES (FREQUENCIES) 334
43 VIBRATIONAL FREQUENCIES (FREQUENCIES)
FREQUENCIES,options,
Calculate harmonic vibrational frequencies and normal modes. The hessian is calculated analytically
or numerically by finite differences in 3N cartesian coordinates (Z-Matrix coordinates
will be destroyed on entry). If analytic gradients are available these are differentiated once to
build the hessian, otherwise the energy is differentiated twice. If for the wavefunction method
dipole moments are available, the dipole derivatives and the IR intensities are also calculated.
Note that numerical hessians cannot be computed when dummy atoms holding basis functions
are present. To get reasonable results it is necessary to do a geometry optimization before using
the frequency calculation.
43.1 Options
The following options are available:
ANALYTICAL
CENTRAL
NUMERICAL
FORWARD
SYMM=AUTO|NO
AUTO
NOAUTO|NOSYM
Use analytical second derivatives of the energy. At present, analytical
second derivatives are only possible for closed shell Hartree-Fock
(HF) and MCSCF wavefunctions without symmetry. It is not yet possible
to calculate IR-intensities analytically. Note that, due to technical
reasons, the analytical MCSCF second derivatives have to be computed
in the MCSCF-program using e.g. multi; cpmcscf,hess
(see MULTI) before they can be used in FREQUENCIES. If analytical
MCSCF second derivatives have been computed using multi;
cpmcscf,hess, FREQUENCIES will use them by default.
Use central differences/high quality force constants (default).
Differentiate the energy twice, using central differences.
Use forward differences/low quality force constants.
During the numerical calculation of the hessian, the symmetry of the
molecule may be lowered. Giving SYMM=AUTO the program uses
the maximum possible symmetry of the molecular wavefunction in
each energy/gradient calculation, and this option therefore minimizes
the computational effort. With SYMM=NO no symmetry is used during
the frequency calculation (default). For single reference calculations
like HF, MP2, CCSD, RCCSD the AUTO option can be safely
used and is recommended. However, the AUTO option cannot be used
for multireference methods (MCSCF/MRCI/ACPF/AQCC/RS2). If
given, the option is disabled in these cases. For these methods frequency
calculations are only possible without symmetry. Symmetry
is turned off atomatically if the state symmetry is 1. Note that this may
fail if there are lower states in other symmetries. Use of RESTRICT,
SELECT, REF, PROJECT, LOCAL, state-averaged MCSCF will lead
on errors unless the calculation is performed in C 1 symmetry In such
cases the whole calculation must be done without symmetry.
Same as SYMM=AUTO, see above.
Same as SYMM=NO, see above.
HESSREC|SAVE=record Save hessian to record. By default the hessian is saved on record
5300.2.