6.11 Software
159
6.11 Software
6.11.1 Calculation of the Anharmonic Force Field
and of the Rovibrational Correction
There are several quantum chemistry programs permitting the calculation of the
force field and the rovibrational corrections. The most used seem to be Gaussian
(Frisch et al. 2016) and CFOUR (Stanton et al. 2011). Furthermore, there are several
programs dedicated to the calculation of the rovibrational corrections from the force
field in Cartesian coordinates up to cubic terms. For instance, SHRINK written by
Sipachev (2004). A similar program was written by Groner and Warren (2001).
6.11.2 Fit of the Internal Coordinates to the Moments
of Inertia
A rather recent computer program, called STRFIT, has many options and is easy to
use. It was developed by Z. Kisiel. It is available from http://www.ifpan.edu.pl/~kis
iel/prospe.htm (Kisiel 2003). This program can fit different types of structure: r 0 , r z ,
r e , and the different r m structures.
One of the weak points of STRFIT is that it does not permit the weighting of data.
A more general package, called MOMSTRUC is from H. D. Rudolph. It is available
from:
https://www.uni-ulm.de/~hrudolph/sw_archiv/MOMSTRUC/. This program is
described in Appendix Va of Rudolph and Demaison (2011).
Recently, a software package called Molecular Structure Refinement (MSR)
permitting the determination of equilibrium structures by means of the semiexperimental approach was described (Mendolicchio et al. 2017). This last program permits
the use of predicate parameters.
6.12 Conclusion
The substitution or r s method has for many decades been the method most often used
to determine structures from moments of inertia, and it is still widely used. However,
this method sometimes gives unstable results and should, therefore, be used with
caution.
The mass-dependent method is a significant improvement over the r s method and
gives satisfactory results for small molecules. However, for large molecules, it fails
unless used in conjunction with the mixed estimation.
159
6.11 Software
6.11.1 Calculation of the Anharmonic Force Field
and of the Rovibrational Correction
There are several quantum chemistry programs permitting the calculation of the
force field and the rovibrational corrections. The most used seem to be Gaussian
(Frisch et al. 2016) and CFOUR (Stanton et al. 2011). Furthermore, there are several
programs dedicated to the calculation of the rovibrational corrections from the force
field in Cartesian coordinates up to cubic terms. For instance, SHRINK written by
Sipachev (2004). A similar program was written by Groner and Warren (2001).
6.11.2 Fit of the Internal Coordinates to the Moments
of Inertia
A rather recent computer program, called STRFIT, has many options and is easy to
use. It was developed by Z. Kisiel. It is available from http://www.ifpan.edu.pl/~kis
iel/prospe.htm (Kisiel 2003). This program can fit different types of structure: r 0 , r z ,
r e , and the different r m structures.
One of the weak points of STRFIT is that it does not permit the weighting of data.
A more general package, called MOMSTRUC is from H. D. Rudolph. It is available
from:
https://www.uni-ulm.de/~hrudolph/sw_archiv/MOMSTRUC/. This program is
described in Appendix Va of Rudolph and Demaison (2011).
Recently, a software package called Molecular Structure Refinement (MSR)
permitting the determination of equilibrium structures by means of the semiexperimental approach was described (Mendolicchio et al. 2017). This last program permits
the use of predicate parameters.
6.12 Conclusion
The substitution or r s method has for many decades been the method most often used
to determine structures from moments of inertia, and it is still widely used. However,
this method sometimes gives unstable results and should, therefore, be used with
caution.
The mass-dependent method is a significant improvement over the r s method and
gives satisfactory results for small molecules. However, for large molecules, it fails
unless used in conjunction with the mixed estimation.