Anti-resonance approach to soft tunnelling centres

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Abstract
In recent years various theoretical methods have been used to handle the fundamental decay problem of the archetypal Hamiltonian in quantum diffusion. In the authors study they determine the fundamental Green function (GF), which governs the decay, by an anti-resonance ansatz and a factorisation procedure beyond Hartree-Fock. The resulting GF is able to satisfy rigorous frame requirements (high-temperature expansions, sum rules, low-temperature laws derived from ab initio calculations). The spectral and temporal decay behaviour according to this GF is discussed for various coupling laws. In the case of 'Ohmic dissipation' (linear power-law coupling) the authors find a cross-over temperature, depending on the coupling strength, above which coherence disappears, the diffusion constant displaying a T+2 alpha -1 behaviour in the intermediate temperature region.