Lang, RobertHickman, Riley J.Zeng, Tao2020-04-172020-04-172020-02-25Computer Physics Communications 247 (February 2020): 106946.https://doi.org/10.1016/j.cpc.2019.106946https://hdl.handle.net/10315/37189An 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.enAttribution-NonCommercial-NoDerivs 2.5 CanadaJahn–TellerPseudo-Jahn–TellerVibronic couplingHamiltonian formalismPythonSymbolic computationArticlehttps://www.sciencedirect.com/journal/computer-physics-communicationshttps://www.elsevier.com/https://www.sciencedirect.com/science/article/pii/S0010465519303029