MOLPRO

47 POTENTIAL ENERGY SURFACES (SURF) 360
rhf
label4
{surf,start1D=label1
vmult,start2D=label1,start3D=label2,multi=4
repar,type=1}
vscf
vci
47.7 Quality Check
CHECK,options
The CHECK directive of the SURF program allows for a quality check of a completed surface.
This routine simply computes the exact ab initio energies at randomly selected grid points and
compares these values with the interpolated ones, which will be used subsequently for the determination
of the wavefunction. This program is fully parallelized.
LEVEL=n
PONTS=value
Denotes the level to be checked, i.e. 1 corresponds to 1D, etc.
Determines the number of grid points in one dimension to be checked.
The default is set to 4.
47.8 Recommendations
It is recommended to
• use the MASS keyword within the geometry specification in order to rotate the molecule
into standard orientation. This is necessary for a full exploitation of symmetry within the
generation of the potential energy surface.
• split up the calculations in three parts: (1) Do a very accurate geometry optimization and
bring the optimized geometry into standard orientation. 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. Later on you can restart your VSCF and VCI calculations
from this external file without recomputing the surface.
• use a 1D: CCSD(T)/vtz, 2D: MP4(SDQ)/vtz and 3D: MP2/vtz multi-level scheme in combination
with symmetry and a parallelized MOLPRO version in order to speed up the calculations.
• reduce the quality of the normal coordinates. If you do not require extremely high accuracy,
it is sufficient to compute the normal coordinates (i.e. the harmonic frequencies) at
the MP2 level rather than the CCSD(T) level. This saves a lot of computer time and the
deviations are usually not larger than 1 or 2 wavenumbers.
47.9 Standard Problems
• Problem:
The SURF calculation crashes with an error message like