MOLPRO

49 THE VSCF PROGRAM (VSCF) 363
49 THE VSCF PROGRAM (VSCF)
VSCF,options
The VSCF program is based on the Watson Hamiltonian
Ĥ = 1 2 ∑ αβ( ˆ J α − ˆπ α )µ αβ ( ˆ J β − ˆπ β ) − 1 8 ∑ α
µ αα − 1 2 ∑ i
∂ 2
∂q 2 i
+V (q 1 ,...,q 3N−6 ) (69)
in which the potential energy surfaces, V (q 1 ,...,q 3N−6 ), are provided by the SURF module.
Vibrational angular momentum terms are switched off by default. Within the grid-based version
of the program the one-dimensional Schrödinger equation is solved by the DVR procedure of
Hamilton and Light. Note that, the number of basis functions (distributed Gaussians) is determined
by the grid points of the potential and cannot be increased without changing the PES
grid representation. In contrast to that the number of basis functions can be modified without
restrictions in the polynomial based version. In all cases the basis is fixed to distributed Gaussians
(DG). As VSCF calculations are extremely fast, these calculations cannot be restarted. For
details see:
G. Rauhut, T. Hrenar, A Combined Variational and Perturbational Study on the Vibrational
Spectrum of P 2 F 4 , Chem. Phys. 346, 160 (2008).
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. 1 2 ∑ αβ ˆπ α µ αβ ˆπ β , 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 µ 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 nonlinear
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
SOLVER=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 × (n − 1)/2 combination
bands consisting of two modes in the first vibrational level.
For solving the one-dimensional Schrödinger equation within a grid
representation two different algorithms can be used. The default, i.e.