Quantum fidelity susceptibility in excited state quantum phase transitions: Application to the bending spectra of nonrigid molecules Khalouf Rivera, Jamil Carvajal Zahera, Miguel Pérez Bernal, Francisco Funding information This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skodowska-Curie grant agreement No 872081 and from the Spanish National Research, Development, and Innovation plan (RDI plan) under the project PID2019-104002GB-C21 (JKR, MC, and FPB) and COOPB20364 (MC) . This work has also been partially supported by the Consejeria de Conocimiento, Investigacion y Universidad, Junta de Andalucia and European Regional Development Fund (ERDF) , refs. SOMM17/6105/UGR (MC and FPB) and UHU-1262561 (JKR and FPB) . We characterize excited state quantum phase transitions in the two dimensional limit of the vibron model with the quantum fidelity susceptibility, comparing the obtained results with the information provided by the participation ratio. As an application, we locate the eigenstate closest to the barrier to linearity and determine the linear or bent character of the different overtones for particular bending modes of six molecular species. We perform a fit and use the optimized eigenvalues and eigenstates in three cases and make use of recently published results for the other three cases. 2022-02-02T13:15:55Z 2022-02-02T13:15:55Z 2022-01-04 info:eu-repo/semantics/article Khalouf-Rivera, J., Carvajal, M., & Perez-Bernal, F. (2022). Quantum fidelity susceptibility in excited state quantum phase transitions: application to the bending spectra of nonrigid molecules. SciPost Physics, 12(1), 002. doi:[10.21468/SciPostPhys.12.1.002] http://hdl.handle.net/10481/72624 10.21468/SciPostPhys.12.1.002 eng info:eu-repo/grantAgreement/EC/H2020/872081 http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España SciPost