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49.1 Options

The following options are available:

TYPE=value

VSCF solutions can be obtained using a potential in grid representation, i.e. TYPE=GRID, or in a polynomial representation, TYPE=POLY. In the latter case the POLY program needs to be called prior to the VSCF program in order to transform the potential.

PMP=value

Vibrational angular momentum terms,
i.e. $\frac{1}{2} \sum_{\alpha\beta} \hat{\pi}_\alpha\mu_{\alpha\beta} \hat{\pi}_\beta$, and the Watson correction term are by default switched off. PMP=1 adds the Watson correction term (see eq. 69) as a pseudo-potential like contribution to the fine grid of the potential. PMP=2 allows for the calculation of the integrals of the PMP operator using the approximation that the $\mu$ tensor is given as the inverse of the moment of inertia tensor at equilibrium geometry. When using PMP=4 the expansion of the effective moment of inertia tensor will be truncated after the 1D terms (rather than the 0D term in case of PMP=2. Note that the values higher than 2 are only active for non-linear molecules. PMP=5 truncates the series after the 2D term. In almost all cases PMP=2 is fully sufficient. Vibrational angular momentum terms are accounted for in a perturbational manner and do not affect the wavefunction.

COMBI=value

By default the VSCF program calculates the fundamental modes of the molecule only. However, choosing COMBI=1 allows for the calculation of the first vibrational overtones and $n\times(n-1)/2$ combination bands consisting of two modes in the first vibrational level.

SOLVER=value

For solving the one-dimensional Schrödinger equation within a grid representation two different algorithms can be used. The default, i.e. SOLVER=1, calls the discrete variable representation (DVR) as proposed by Hamilton and Light. Alternatively, the collocation algorithm of Young and Peet can be used (SOLVER=2).

THERMO=value

THERMO=1 allows for the improved calculation of thermodynamical quantities (compare the THERMO keyword in combination with a harmonic frequency calculation). However, the approach used here is an approximation: While the harmonic approximation ist still retained in the equation for the partition functions, the actual values of the frequencies entering into these functions are the anharmonic values derived from the VSCF calculation.

ROTJ=value

Rovibrational levels can be computed in an approximative fashion only (this does not work in combination with the COMBI option). Once the VSCF equations have been solved, the rotational constants will be computed from the vibrationally averaged structures for each vibrational level. This allows for a rough estimate and very fast calculation of the rovibrational levels. ROTJ=$n$ determines the value of $J$. A negative number for $J$ results in a calculation of all rovibrational levels from $J=1$ up to the specified $J$ value.

DIPOLE=value

DIPOLE=1 allows for the calculation of infrared intensities. Calculation of infrared intensities requires the calculation of dipole surfaces within the SURF program. By default intensities will not be computed.

NDIM=value

The expansion of the potential in the VSCF calculation can differ from the expansion in the SURF calculation. However, only values less or equal to the one used in the surface calculation can be used.

NBAS=value

The number of basis functions (distributed Gaussians) to be used for solving the VSCF equations can controlled by NBAS=value. The default is NBAS=20. This option is only active once a polynomial representation of the potential has been chosen, see the option TYPE=POLY and the POLY program.

ORDPOL=val

Once the default value has been changed in the POLY program, this value needs to be changed here as well.

ORDPROD=val

Once the default value has been changed in the POLY program, this value needs to be changed here as well.

SHOW=value

SHOW=1 prints the effective 1D polynomials in case that the potential is represented in terms of polynomials, see the option TYPE=POLY and the POLY program.

INFO=value

INFO=1 provides a list of the values of all relevant program parameters (options).

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