MOLPRO

50 THE VCI PROGRAM (VCI) 367
DIAG=value
INFO=value
in the VSCF program. 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.
In the polynomial configuration selective VCI program different diagonalization
schemes can be used. DIAG=CON specifies a conventional
non-iterative diagonalization as used in the grid-based versions.
DIAG=JAC is the default and uses a Jacobi-Davidson scheme. DIAG=HJD
denotes a disk-based Jacobi-Davidson algorithm.
INFO=1 provides a list of the values of all relevant program parameters
(options).
50.2 Recommendations
It is recommended to split up the calculations in three parts: (1) Do a very accurate geometry
optimization and bring the optimized geometry into standard orientation (using the MASS
keyword. Start a second calculation based on the optimized geometry and do (2) a harmonic
frequency calculation which should be stored in the restart-file (.wfu). Make a backup of the
restart-file. (3) Start a SURF, VSCF and VCI calculation from the restart-file (.wfu) and dump
the potential energy surfaces to an external file (using the DUMP keyword). Later on you can
restart your VSCF and VCI calculations from this external file without recomputing the surface.
50.3 Examples
The following input example (1) optimizes the geometry of water, (2) computes the harmonic
frequencies, (3) generates a potential energy surface around the equilibrium structure, (4) computes
the nuclear wave function and the infrared intensities at the VSCF level, and finally (5)
performs three different VCI calculations using different configuration selection schemes. Vibrational
angular momentum terms are included.
memory,20,m
basis=vdz
orient,mass
geomtyp=xyz
geometry={
3
Water
O 0.0675762564 0.0000000000 -1.3259214590
H -0.4362118830 -0.7612267436 -1.7014971211
H -0.4362118830 0.7612267436 -1.7014971211
}
hf
mp2
optg
{frequencies,symm=auto
print,low=50}
label1
{hf
start,atden}
{mp2
cphf,1}