Dresden 2011 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 91: Joint Focussed Session: Theory and Computation of Electronic Structure: New Frontiers VIII

HL 91.5: Talk

Friday, March 18, 2011, 12:30–12:45, TRE Phy

Selective Excitation of Molecular Vibrations by Tunneling Electrons — •Jessica Walkenhorst¹, Marius Wanko¹, Alberto Castro², and Angel Rubio¹ — ¹Nano-Bio Spectroscopy group and ETSF Scientific Development Centre, Dpto. Física de Materiales, Universidad del País Vasco, Centro de Física de Materiales CSIC-UPV/EHU-MPC and DIPC, San Sebastián, Spain — ²Institute for Biocomputation and Physics of Complex Systems (BIFI), University of Zaragoza, Spain

Tunneling electrons can be used to excite vibrations in molecules. By combining scanning electron microscopy (STM) with inelastic electron tunneling spectroscopy (IETS) one can obtain vibrational spectra of single molecules adsorbed on a surface. Interestingly in large molecules the vibrational spectrum depends on the impact point of the electrons on the molecular surface. Selective excitation of vibrational modes by the STM tip has been proposed to explain these experimental findings (the so-called 'excitation of local vibrations' model). Therefore, we want to simulate the dynamical response of Schiff base (CNH4+) to tunneling electrons. To this end, we perform molecular dynamics simulations based on time-dependent density functional theory (TDDFT). Vibrational spectra are then obtained by Fourier analysis of the velocity autocorrelation function. This way, we study the relative strength of the excited molecular vibrations in dependence on the impact point of the tunneling electrons. Finally, a comparison between numerical results and experimental findings is attempted and the validity of the 'excitation of local vibrations' model is discussed.