Construction of accurate multi-sheeted multi-dimensional potential-energy surfaces and calculation of nonadiabatic quantum dynamics for selected four-, five- and six-atomic molecules
Final Report Abstract
The established theory of the static and dynamic Jahn-Teller (JT) and pseudo JT (PJT) effects, which is based on a Taylor expansion of the diabatic potential-energy (PE) surfaces in normal-mode displacements up to second order, has been extended by a systematic expansion of diabatic JT/PJT PE surfaces in symmetry-adapted polynomials up to high orders. We developed and applied these techniques for the examples of the E x e JT effect in P4+ and several transition-metal trifluorides, the (E + A) x (e + a) JT/PJT effect in NH3+ and PH3+, as well as the T2 x t2 JT effect in CH4+. For comparatively simple cases, such as the E x e JT effects in P4+ and transition-metal trifluorides, it was shown that a 6th order expansion yields accurate analytic PE surfaces in the relevant range of nuclear coordinates. In more challenging cases, such as the (E + A) x (e + a) JT/PJT effect in NH3+, PH3+ and the T2 x t2 JT effect in CH4+, expansions up to 8th order were found to be necessary. The nonadiabatic nuclear dynamics of these systems was treated with numerical wave-packet propagation methods, using either harmonic-oscillator or discrete-variable basis sets. The vibronic structure of the photoelectron spectra of P4, NH3 and PH3 was calculated with these methods. For the transition-metal trifluorides, electronic absorption/emission spectra and IR absorption spectra were calculated. For all spectra, the relevance of JT couplings beyond second order was demonstrated. The multi-sheeted multi-dimensional ab initio PE surfaces developed in the present work are available upon request and can be used for future benchmarking of approximate methods for the treatment of nonadiabatic nuclear dynamics, such as, for example, quasiclassical surface-hopping trajectory methods. The proposed construction of a full-dimensional three-sheeted ab initio PE surface for the N, V, Z valence states of ethylene remains desideratum. Meanwhile, the collaboration of H.-D. Meyer (Heidelberg) with F. Gatti (Montpellier) made substantial progress with the construction of analytic PE surfaces and the calculation of absorption spectra for ethylene.
