VPT2-screened PyVCI

The VPT2-screened PyVCI program package is a general purpose open-source code for simulating accurate molecular spectra, based upon force field expansions of the potential energy surface in normal mode coordinates. It includes harmonic normal coordinate analysis, vibrational perturbation theory and vibrational configuration interaction (VCI) algorithms, with VCI matrix elements chosen iteratively according to VPT2 energy contributions, across a range of significance thresholds. It is implemented primarily in Python for accessibility but with time-consuming routines written in C (produced using Cython).

Force fields for use with this program package may be obtained from the extensible PyPES library of high quality analytical potential energy surfaces (http://sourceforge.net/projects/pypes-lib-ext).