PyVCI

The 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 and vibrational configuration interaction (VCI) algorithms, implemented primarily in Python for accessibility but with time-consuming routines written in C. Coriolis coupling terms may be optionally included in the vibrational Hamiltonian.

Quartic force fields are obtained from the PyPES library of high quality analytical potential energy surfaces (http://sourceforge.net/projects/pypes-lib) or by numerical differentiation of analytic second derivatives generated using the GAMESS quantum chemical program package (http://www.msg.ameslab.gov/gamess/).