An increasing number of studies in Jahn–Teller and pseudo-Jahn–Teller effects have revealed the importance of vibronic Hamiltonians with high order expansions in vibrational coordinates. This motivates us to present VHEGEN (V-ibronic H-amiltonian E-xpansion GEN-erator), a Python package that is capable of symbolically generating arbitrarily high order expansion formulas for the vibronic Hamiltonians. The program covers all >6000 bimodal Jahn–Teller and pseudo-Jahn–Teller problems in trigonal and tetragonal symmetries. The generated expansions are correct, complete, and concise. VHEGEN is a useful program for future studies in Jahn–Teller and pseudo-Jahn–Teller effects. Program summary: Program Title: VHEGEN Program Files doi: Licensing provisions: GPLv3 Programming language: Python Nature of problem: Obtaining correct, complete, and concise high-order expansions of Jahn–Teller and pseudo-Jahn–Teller Hamiltonians in a case-by-case manner is a laborious and error-prone task. Solution method: We present a Python package to automate the utilization of our recently developed formalisms in obtaining any possible trigonal and tetragonal bimodal (pseudo-)Jahn–Teller vibronic Hamiltonian expanded to arbitrary order in vibrational coordinates.

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Computer Physics Communications
Department of Chemistry

Lang, R.A. (Robert A.), Hickman, R.J. (Riley J.), & Zeng, T. (2019). VHEGEN: A vibronic Hamiltonian expansion generator for trigonal and tetragonal polyatomic systems. Computer Physics Communications. doi:10.1016/j.cpc.2019.106946