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By computing the non-adiabatic coupling terms and the adiabatic-to-diabatic transformation angle along closed contours in nuclear configuration space using the CASSCF method and the aug-cc-pVTZ basis set for the lowest three electronic states of HeH2+, we explore the conical intersection between states in near collinear and noncollinear geometries, particularly in the C2v geometry. [ABSTRACT FROM AUTHOR]

In order to explore spectroscopic properties of a floppy molecule, it is necessary to compute accurate diabatic potential energy surfaces (PESs) around the Franck–Condon region of nuclear configuration space. In such cases, it is desirable to include the non-adiabatic coupling terms (NACTs) through Jahn–Teller (JT) and pseudo Jahn–Teller (PJT) effects as well as other accidental conical intersections (CIs) prevailing among the electronic states of the molecule. In this work, we investigate NACTs among the five lowest doublet electronic states of NO3radical [and 22B2)], in which all those effects (JT, PJT and CIs) have prominent contributions. The study is carried out in terms of normal modes (Qis) of NO3and the CIs (JT and accidental) are located in a plane of nuclear configuration space of two such coordinates (QiandQj). We have calculatedab initioadiabatic PESs and NACTs of those five states of NO3at the MRCI level as functions of pairwiseQis. Further, to explore the nature of a given CI in terms of normal coordinates contributing to NACTs within a particular planeQi-Qj, we have performed CP-MCSCF study computing analytic NACTs and characterised their contributions along variousQks. [ABSTRACT FROM PUBLISHER]

We are investigating the molecular dynamics of the allene system using a parallelised Time Dependent Discrete Variable Representation (TDDVR) methodology by employing a corresponding cation ( [image omitted]) where its two electronic surfaces (A2E and B2B2) are vibronically coupled with each other. In fact the allene radical cation exhibits a three-surface system due to the presence of degeneracy in the A2E state. Our initial investigation is carried out on a linear vibronically coupled model Hamiltonian consisting of 11 vibrationally active modes with two potential energy surfaces. We included both the bilinear and quadratic coupled terms in the effective three-surface Hamiltonian of the [image omitted] radical cation. The spectral profiles obtained from the higher order Hamiltonian show better agreement with the experimental spectrum than the result corresponding to the linearly coupled one. Along with the spectral calculation, we also analyse the nuclear cum population dynamics of the same system. The TDDVR calculated spectral profile as well as the population dynamics show reasonably good agreement with the results calculated by an exact quantum mechanical (multiconfiguration time-dependent Hartree, MCTDH) approach as well as experimental measurement. It appears that the TDDVR approach for those large systems where the quantum mechanical description is needed in a restricted region, is a good compromise between accuracy and speed. [ABSTRACT FROM AUTHOR]

By computing the non-adiabatic coupling terms and the adiabatic-to-diabatic transformation angle along closed contours in nuclear configuration space using the CASSCF method and the aug-cc-pVTZ basis set for the lowest three electronic states of HeH2+, we explore the conical intersection between states in near collinear and noncollinear geometries, particularly in the C2v geometry. [ABSTRACT FROM AUTHOR]