  iGVPT2 is a program for computing anharmonic corrections to vibration
frequencies, based on force field expansion of the potential energy surface in
normal mode coordinates. It includes second order vibrational perturbation
theory (VPT2) algorithm and its derived methods (VPT2+K, DCPT2, HDCPT2). iGVPT2
is interfaced with several computation chemistry packages to compute the
potential energies and dipoles derivatives. The second, third and quartic
derivatives can be computed at the same level of theory but they can be also
computed using different methods via one or two computational packages. iGPVT2
includes also a very fast hybrid QM//MM approach for biomolecules. It is
provided free-of-charge for non-commercial research (see
\url{https://sites.google.com/site/allouchear/igvpt2}).
