The PESTRANS program allows to change the coordinate system being used within the representation of the potential
by a Duschinsky-like transformation. This allows for the transformation of PESs as needed for the calculation of the vibrational spectra of
isotopologues or Franck-Condon factors including Duschinsky rotations. For further details see:
P. Meier, D. Oschetzki, R. Berger, G. Rauhut, Transformation of potential energy surfaces for estimating isotopic shifts
in anharmonic vibrational frequency calculations, J. Chem. Phys. 140, 184111 (2014).
The following options are available:
- By default the Eckart transformation matrix needed within the PESTRANS program will be computed explicitly. ECKART=0 replaces
the Eckart transformation matrix by a unit matrix.
- As needed for Franck-Condon calculations, UMAT=1 defines the linear combinations of the displacement vectors due to Duschinsky rotations,
which influences the selection of states in subsequent VCI calculations. The default, UMAT=0, switches off this feature.
- Once vibrational-rotational coupling surfaces have been computed in the SURF program, these
couplings can be considered (VRC=1) or excluded (VRC=0, default) in the PESTRANS program. The inclusion of these
terms usually increases the accuracy of the transformation.
- CUT=0 (default) transforms all surfaces as requested by the input. CUT=1 neglects the generation of vibrational-rotational
coupling surfaces for the new potential. CUT=2 neglects rotational-rotational coupling surfaces within the transformation and thus
also for the new potential.
- Elements in the displacement vectors below this threshold (default THRQ=10) will be neglected within the transformation.
- Threshold controlling the analysis of the S-matrix indicating the accuracy of the transformation (default: THRMATS=0.3).
Most keywords and directives of the SURF program can also be used in the PESTRANS program
(i.e. NDIM, SCALE, INFO, INTENSITY, SCALNM, DISK, LINCOMB),
while specific ones had to be excluded (i.e. NGRID, etc. ).