The role of electron–nuclear coupling on multi-state photoelectron spectra, scattering processes and phase transitions

Abstract

We present first principle based beyond Born-Oppenheimer (BBO) theory and its applications on various models as well as realistic spectroscopic and scattering processes, where the Jahn-Teller (JT) theory is brought...

Construction of Beyond Born‐Oppenheimer Based Diabatic Surfaces and Generation of Photoabsorption Spectra: The Touchstone Pyrazine (C4N2H4)

“…Our earlier studies [22,[63][64][65][66][67][68]76,90] have firmly established that if the adiabatic PESs and NACTs exhibit even-parity functional forms along some nuclear DOFs, the associated diabatic PESs and couplings also retain the (even) parity. Such unique feature is observed along one of the components in most of the degenerate pair of asymmetric stretching/bending modes or even some specific non-degenerate normal modes.…”

“…Later on, Adhikari and coworkers [38,39,62,63] have generalized the BBO formalism by deriving explicit forms of various ADT quantities (ADT equations, NACTs, curl-divergence equations and diabatic PESs matrix elements) and developed a program package, 'ADT' [64] to formulate those quantities as well as to evaluate the numerical solutions for any (N) coupled electronic manifold with M nuclear degrees of freedom (DOFs). Such a complete theory has been successfully applied on various floppy molecules of spectroscopic interest [62,63,[65][66][67][68] and also on several triatomic scattering processes. [67][68][69][70][71] In this article, when highly accurate BBO based diabatic PESs matrix of pyrazine employing ab initio calculated adiabatic PESs and NACTs are calculated over six nuclear planes comprising of four nonadiabatically active normal modes (Q 1 , Q 6a , Q 9a and Q 10a ), those are used to carry out multi-state (electronic) multi-dimensional (vibrational) quantum dynamics with the aid of TDDVR approach.…”

“…Such a complete theory has been successfully applied on various floppy molecules of spectroscopic interest [62,63,[65][66][67][68] and also on several triatomic scattering processes. [67][68][69][70][71] In this article, when highly accurate BBO based diabatic PESs matrix of pyrazine employing ab initio calculated adiabatic PESs and NACTs are calculated over six nuclear planes comprising of four nonadiabatically active normal modes (Q 1 , Q 6a , Q 9a and Q 10a ), those are used to carry out multi-state (electronic) multi-dimensional (vibrational) quantum dynamics with the aid of TDDVR approach. TDDVR is advantageous from the computational point of view due to blending of classical and quantum dynamics leading to requirement of lesser number of basis functions (grid points) for each nuclear DOF as compared to Fast-Fourier Transformation (FFT) based algorithms.…”

Jahn–Teller Effect in Orthorhombic Manganites: Ab Initio Hamiltonian and Roto-vibrational Spectrum

“…It is important to mention that the NACTs are generally sharp functions with singularities at the close neighborhood of degenerate or near-degenerate point(s)/seam(s) , over the nuclear configuration space (CS). In this context, Baer proposed first principle based “accurate” adiabatic-to-diabatic transformation (ADT) formalism involving the line integral over NACTs. − Later on, Adhikari et al have generalized such ADT approach for any three or more coupled electronic states ,− by carrying out a thorough analysis of the NACT expressions, ADT equations, curl-divergence equations, and diabatic potential energy matrix elements. The workability of such a complete theory has been explored for performing nonadiabatic quantum dynamics on realistic prototypical systems of spectroscopic interest ,− ,, as well as triatomic scattering systems. ,,− In order to carry out “accurate” multistate (electronic) multidimensional (vibrational) quantum dynamics, Adhikari and co-workers − employed time-dependent discrete variable representation (TDDVR) methodology for generating high resolution spectral envelops of molecular systems. ,− …”

“…59−62 Later on, Adhikari et al have generalized such ADT approach for any three or more coupled electronic states 37,63−69 by carrying out a thorough analysis of the NACT expressions, ADT equations, curl-divergence equations, and diabatic potential energy matrix elements. The workability of such a complete theory has been explored for performing nonadiabatic quantum dynamics on realistic prototypical systems of spectroscopic interest 37,[65][66][67][68]70,71 as well as triatomic scattering systems. 67,68,72−74 In order to carry out "accurate" multistate (electronic) multidimensional (vibrational) quantum dynamics, Adhikari and co-workers 75−79 ology for generating high resolution spectral envelops of molecular systems.…”