Current versus temperature-induced switching of a single molecule: Open-system density matrix theory for 1,5-cyclooctadiene on Si(100)

Abstract

The switching of single cyclooctadiene molecules chemisorbed on a Si(100) surface between two stable conformations, can be achieved with a scanning tunneling microscope [Nacci et al., Phys. Rev. B 77, 121405(R) (2008)]. Recently, it was shown by quantum chemical and quantum dynamical simulations that major experimental facts can be explained by a single-mode model with switching enforced by inelastic electron tunneling (IET) excitations and perturbed by vibrational relaxation [Nacci et al., Nano Lett. 9, 2997 (2009)]. In the present paper, we extend the previous theoretical work in several respects: (1) The model is generalized to a two-mode description in which two C(2)H(4) units of COD can move independently; (2) contributions of dipole and, in addition, (cation and anion) resonance-IET rates are considered; (3) the harmonic-linear vibrational relaxation model used previously is generalized to anharmonic vibrations. While the present models highlight generic aspects of IET-switching between two potential minima, they also rationalize specific experimental findings for COD/Si(100): (1) A single-electron excitation mechanism with a linear dependence of the switching rate on tunneling current I, (2) the capability to switch both at negative and positive sample biases, and (3) a crossover temperature around ~60 K from an IET-driven, T-independent atom tunneling regime, to classical over-the-barrier isomerization with exponential T-dependence at higher temperatures for a bias voltage of +1.5 V and an average tunneling current of 0.73 nA.

Probing quantum coherence in ultrafast molecular processes: An ab initio approach to open quantum systems

“…Most of them use ab initio results as input for master-equation approaches. 69,70 Stochastic approaches have been used in the context of TDDFT, at various level of complexity. 45,[71][72][73] The proposed approach is alternative to both, avoiding the possible artifacts of TDDFT beyond the linear regime [74][75][76][77] and defining a seamless integration of ab initio and open-quantum systems approaches.…”

Desorption induced by low energy charge carriers on Si(111)‐7 × 7: First principles molecular dynamics for benzene derivates

“…Here, electrons or holes often transiently occupy short lived donor or acceptor states at the adsorption site, so called ion resonances. The manipulation via such ion resonances or the simulations of such experiments can be divided into the below and the above threshold regime, depending on the bias voltage. In the above threshold case, the voltage can create charge carriers with an energy larger than the resonance energy.…”

Quantum Chemical Cluster Models for Chemi- and Physisorption of Chlorobenzene on Si(111)-7×7

“…This result was computed within a cluster model for the silicon surface and the adsorbate, applying first-principles quantum chemistry methods. Although a cluster moldel is only applicable to surfaces of semiconductors and insulators, the required quantities for the calculation of inelastic electron tunneling (IET) rates , are easily accessible (see, e.g., refs and ). For the current system we also want to use our results to simulate the highly local process of STM experiments as a second step.…”