**ANALYTICAL**- 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.
**CENTRAL**- Use central differences/high quality force constants (default).
**NUMERICAL**- Differentiate the energy twice, using central differences.
**FORWARD**- Use forward differences/low quality force constants (only effective if gradients are available).
**SYMM=AUTO|NO**- 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 symmetry In such cases the whole calculation must be done without symmetry.
**AUTO**- Same as SYMM=AUTO, see above.
**NOAUTO|NOSYM**- Same as SYMM=NO, see above.
**HESSREC|SAVE=***record*- Save hessian to
*record*. By default the hessian is saved on record 5300.2. **FREQREC=***record*- Save frequencies and normal modes to
*record*(default 5400.2) This information is used, e.g., by the VSCF/VCI program. **TASKREC=***record*- Save task information in numerical hessian calculation to the given record. This information is required for a restart of a numerical hessian calculation. By default, the information is saved on record 5500.2.
**READ**- Read hessian from default hessian record.
**READ|START=***record*- Use hessian from previously saved on
*record*. If the hessian has been computed for the current method and geometry already, it is used by default. **RESTART**- Attempt to restart a previous numerical frequency/hessian calculation using default task record.
**RESTART=***record*- Attempt to restart a previous numerical frequency/hessian calculation using task record
*record*. **LOW=***value*- Threshold for printing low frequencies in cm. If this option is given, frequencies below the given value are not printed. By default, all frequencies are printed.
**STEP=***value*- Determines the step size of the numerical differentiation of the energy or the gradient. The default step size is 0.01 a.u.
**MAXTASK=***value*- Stop the calculation if the number of tasks is exceeded (the calculation can be restarted later).
**MAXCPU=***value*- Stop the calculation if the given CPU-time (in sec) exceeded (the calculation can be restarted later).
**NEW**- Recompute hessian, even if a hessian is already available.
**PROJECT**- Project rotations and translations out of the hessian (default).
**NOPROJECT**- Don't project rotations and translations out of the hessian.
**PRINT=***value*- Print option. If
*value*is greater or equal to zero, the hessian and other information is printed (default ). **DEBUG**- Print Debug information, same as PRINT=1.
**SCALE=***value*- Scaling factor for frequencies. The scaled frequencies are used to compute the ZPE and thermodynamic properties.

For compatibility with older MOLPRO versions many of the options can also be set using directives, as described in the following sections.

molpro@molpro.net 2019-09-18