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:

`ECKART`=*n*- 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. `UMAT`=*n*- 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. `VRC`=*n*- 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`=*n*`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.`THRQ`=*value*- Elements in the displacement vectors below this threshold (default
`THRQ=10`) will be neglected within the transformation. `THRMATS`=*value*- 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. ).

manual quickstart instguide update basis

molpro@molpro.net 2018-03-17