@article{MalicWeberRichteretal.2011, author = {Malic, E. and Weber, C. and Richter, M. and Atalla, V. and Klamroth, Tillmann and Saalfrank, Peter and Reich, Sebastian and Knorr, A.}, title = {Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.097401}, pages = {4}, year = {2011}, abstract = {The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photoswitches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable redshift of transition energies depending on the switching state of the spiropyran molecule. Our results suggest that carbon nanotubes are excellent substrates for the optical readout of spiropyran-based molecular switches. The gained insights can be applied to other noncovalently functionalized one-dimensional nanostructures in an externally induced dipole field.}, language = {en} } @article{FlossKlamrothSaalfrank2011, author = {Floss, Gereon and Klamroth, Tillmann and Saalfrank, Peter}, title = {Laser-controlled switching of molecular arrays in an dissipative environment}, series = {Physical review : B, Condensed matter and materials physics}, volume = {83}, journal = {Physical review : B, Condensed matter and materials physics}, number = {10}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.83.104301}, pages = {9}, year = {2011}, abstract = {The optical switching of molecular ensembles in a dissipative environment is a subject of various fields of chemical physics and physical chemistry. Here we try to switch arrays of molecules from a stable collective ground state to a state in which all molecules have been transferred to another stable higher-energy configuration. In our model switching proceeds through electronically excited intermediates which are coherently coupled to each other through dipolar interactions, and which decay incoherently within a finite lifetime by coupling to a dissipative environment. The model is quite general, but parameters are chosen to roughly resemble the all-trans -> all-cis isomerization of an array of azobenzene molecules on a surface. Using analytical and optimal control pulses and the concept of "laser distillation," we demonstrate that for various aggregates (dimers up to hexamers), controlled and complete switching should be possible.}, language = {en} } @article{WirthMonturetKlamrothetal.2011, author = {Wirth, Jonas and Monturet, Serge and Klamroth, Tillmann and Saalfrank, Peter}, title = {Adsorption and (photo-) electrochemical splitting of water on rutile ruthenium dioxide}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {93}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {6}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/93/68001}, pages = {6}, year = {2011}, abstract = {In this work, the adsorption and splitting of the water molecule by light and/or an external potential is investigated in the frame of (photo-) electrochemical cells using a rutile ruthenium dioxide anode. With the help of periodic density functional calculations, the adsorbed structures of H(2)O and some radicals involved in the splitting process (O, OH, OOH) are obtained and compared with the available experimental results. On the basis of these electronic-structure calculations, we use a method to calculate the stability of the reaction intermediates and conclude on the thermodynamical possibility of the water splitting reaction at the surface. We demonstrate that a moderate overpotential of 0.64 V is required for the reaction to take place at the RuO(2)(110) surface.}, language = {en} } @article{KlinkuschKlamrothSaalfrank2009, author = {Klinkusch, Stefan and Klamroth, Tillmann and Saalfrank, Peter}, title = {Long-range intermolecular charge transfer induced by laser pulses : an explicitly time-dependent configuration interaction approach}, issn = {1463-9076}, doi = {10.1039/B817873a}, year = {2009}, abstract = {In this paper, we report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (TD-CIS) approach. The method is capable of describing explicitly time-dependent phenomena beyond perturbation theory and is systematically improvable. In contrast to most time-dependent density functional methods it also allows us to treat long-range charge-transfer states properly. As an example, the laser-pulse induced charge transfer between a donor (ethylene) and an acceptor molecule (tetracyanoethylene, TCNE) is studied by means of TD-CIS. Also, larger aggregates consisting of several donors and/or acceptors are considered. It is shown that the charge distribution and hence the dipole moments of the systems under study are switchable by (a series of) laser pulses which induce selective, state-to-state electronic transitions.}, language = {en} } @article{TremblayKrauseKlamrothetal.2010, author = {Tremblay, Jean Christophe and Krause, Pascal and Klamroth, Tillmann and Saalfrank, Peter}, title = {Time-dependent response of dissipative electron systems}, issn = {1050-2947}, doi = {10.1103/Physreva.81.063420}, year = {2010}, abstract = {We present a systematic study of the influence of energy and phase relaxation on dynamic polarizability simulations in the linear response regime. The nonperturbative approach is based on explicit electron dynamics using short laser pulses of low intensities. To include environmental effects on the property calculation, we use the time- dependent configuration-interaction method in its reduced density matrix formulation. Both energy dissipation and nonlocal pure dephasing are included. The explicit treatment of time-resolved electron dynamics gives access to the phase shift between the electric field and the induced dipole moment, which can be used to define a useful uncertainty measure for the dynamic polarizability. The nonperturbative treatment is compared to perturbation theory expressions, as applied to a simple model system, the rigid H-2 molecule. It is shown that both approaches are equivalent for low field intensities, but the time-dependent treatment provides complementary information on the phase of the induced dipole moment, which allows for the definition of an uncertainty associated with the computation of the dynamic polarizability in the linear response regime.}, language = {en} } @article{KlinkuschSaalfrankKlamroth2009, author = {Klinkusch, Stefan and Saalfrank, Peter and Klamroth, Tillmann}, title = {Laser-induced electron dynamics including photoionization : a heuristic model within time-dependent configuration interaction theory}, issn = {0021-9606}, doi = {10.1063/1.3218847}, year = {2009}, abstract = {We report simulations of laser-pulse driven many-electron dynamics by means of a simple, heuristic extension of the time-dependent configuration interaction singles (TD-CIS) approach. The extension allows for the treatment of ionizing states as nonstationary states with a finite, energy-dependent lifetime to account for above-threshold ionization losses in laser-driven many-electron dynamics. The extended TD-CIS method is applied to the following specific examples: (i) state-to-state transitions in the LiCN molecule which correspond to intramolecular charge transfer, (ii) creation of electronic wave packets in LiCN including wave packet analysis by pump-probe spectroscopy, and, finally, (iii) the effect of ionization on the dynamic polarizability of H-2 when calculated nonperturbatively by TD-CIS.}, language = {en} } @article{KrauseKlamrothSaalfrank2005, author = {Krause, Pascal and Klamroth, Tillmann and Saalfrank, Peter}, title = {Time-dependent configuration-interaction calculations of laser-pulse-driven many-electron dynamics : Controlled dipole switching in lithium cyanide}, issn = {0021-9606}, year = {2005}, abstract = {We report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (doubles) approach. The method accounts for the correlation of ground and excited states, is capable of describing explicitly time-dependent, nonlinear phenomena, and is systematically improvable. Lithium cyanide serves as a molecular test system in which the charge distribution and hence the dipole moment are shown to be switchable, in a controlled fashion, by (a series of) laser pulses which induce selective, state-to-state electronic transitions. One focus of our time-dependent calculations is the question of how fast the transition from the ionic ground state to a specific excited state that is embedded in a multitude of other states can be made, without creating an electronic wave packet. (c) 2005 American Institute of Physics}, language = {en} } @article{AndrianovKlamrothSaalfranketal.2005, author = {Andrianov, Igor V. and Klamroth, Tillmann and Saalfrank, Peter and Bovensiepen, U. and Gahl, Cornelius and Wolf, M. M.}, title = {Quantum theoretical study of electron solvation dynamics in ice layers on a Cu(111) surface}, issn = {0021-9606}, year = {2005}, abstract = {Recent experiments using time- and angle-resolved two-photon photoemission (2PPE) spectroscopy at metal/polar adsorbate interfaces succeeded in time-dependent analysis of the process of electron solvation. A fully quantum mechanical, two-dimensional simulation of this process, which explicitly includes laser excitation, is presented here, confirming the origin of characteristic features, such as the experimental observation of an apparently negative dispersion. The inference of the spatial extent of the localized electron states from the angular dependence of the 2PPE spectra has been found to be non-trivial and system-dependent. (C) 2005 American Institute of Physics}, language = {en} } @article{NacciFoelschZenichowskietal.2009, author = {Nacci, Christophe and Foelsch, Stefan and Zenichowski, Karl and Dokic, Jadranka and Klamroth, Tillmann and Saalfrank, Peter}, title = {Current versus temperature-induced switching in a single-molecule tunnel junction : 1,5 cyclooctadiene on Si(001)}, issn = {1530-6984}, doi = {10.1021/Nl901419g}, year = {2009}, abstract = {The biconformational switching of single cyclooctadiene molecules chemisorbed on a Si(001) surface was explored by quantum chemical and quantum dynamical calculations and low-temperature scanning tunneling microscopy experiments. The calculations rationalize the experimentally observed switching driven by inelastic electron tunneling (IET) at 5 K. At higher temperatures, they predict a controllable crossover behavior between IET-driven and thermally activated switching, which is fully confirmed by experiment.}, language = {en} } @article{ZenichowskiDokicKlamrothetal.2012, author = {Zenichowski, Karl and Dokic, Jadranka and Klamroth, Tillmann and Saalfrank, Peter}, title = {Current versus temperature-induced switching of a single molecule - open-system density matrix theory for 1,5-cyclooctadiene on Si(100)}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {136}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {9}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.3692229}, pages = {13}, year = {2012}, 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 , 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 , 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 C2H4 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 similar to 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.}, language = {en} } @article{FuechselTremblayKlamrothetal.2012, author = {F{\"u}chsel, Gernot and Tremblay, Jean Christophe and Klamroth, Tillmann and Saalfrank, Peter}, title = {Selective excitation of molecule-surface vibrations in H2 and D2 dissociatively adsorbed on Ru(0001)}, series = {Israel journal of chemistry}, volume = {52}, journal = {Israel journal of chemistry}, number = {5}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0021-2148}, doi = {10.1002/ijch.201100097}, pages = {438 -- 451}, year = {2012}, abstract = {In this contribution we report about the selective vibrational excitation of H2 and D2 on Ru(0001) as an example for nonadiabatic coupling of an open quantum system to a dissipative environment. We investigate the possibility of achieving state-selective vibrational excitations of H2 and D2 adsorbed on a Ru(0001) surface using picosecond infrared laser pulses. The systems behavior is explored using pulses that are rationally designed and others that are optimized using a time-local variant of Optimal Control Theory. The effects of dissipation on the laser-driven dynamics are studied using the reduced-density matrix formalism. The non-adiabatic couplings between adsorbate and surface are computed perturbatively, for which our recently introduced state-resolved anharmonic rate model is used. It is shown that mode- and state-selective excitation can be achieved in the absence of dissipation when using optimized laser pulses. The inclusion of dissipation in the model reduces the state selectivity and the population transfer yield to highly excited states. In this case, mode activation is most effectively realized by a rational pulse of carefully chosen duration rather than by a locally optimized pulse.}, language = {en} } @article{SaalfrankKlamrothHuberetal.2005, author = {Saalfrank, Peter and Klamroth, Tillmann and Huber, C. and Krause, Pascal}, title = {Laser-driven electron dynamics at interfaces}, issn = {0021-2148}, year = {2005}, abstract = {In this paper we present time-dependent, quantum-dynamical simulations of photoinduced processes at solid surfaces involving nonadiabatic transitions of electrons to and from short-lived intermediate excited states. In particular, two-photon photoemission (2PPE) spectra of naked metal surfaces and free-standing metal films are considered. One major problem in both cases is the presence of electron-electron scattering, which is treated here in various ways. The first way is to adopt an open-system density matrix approach, in which a single electron is weakly coupled to a "bath" of other electrons. The second approach is based on a many-electron Schrodinger equation, which is solved with the help of a time-dependent configuration interactions singles (TD-CIS) method}, language = {en} } @article{SchwarzeDoscheFlehretal.2010, author = {Schwarze, Thomas and Dosche, Carsten and Flehr, Roman and Klamroth, Tillmann and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Saalfrank, Peter and Cleve, Ernst and Buschmann, Hans-J{\"u}rgen and Holdt, Hans-J{\"u}rgen}, title = {Combination of a CT modulated PET and an intramolecular excimer formation to quantify PdCl2 by large fluorescence enhancement}, issn = {1359-7345}, doi = {10.1039/B919973j}, year = {2010}, abstract = {The [6.6](9,10)anthracenophane 1 (Scheme 1) is a selective fluoroionophore for the detection of PdCl2 with a large fluorescence enhancement factor (I/I-0 > 250).}, language = {en} } @article{NestKlamrothSaalfrank2005, author = {Nest, Mathias and Klamroth, Tillmann and Saalfrank, Peter}, title = {The multiconfiguration time-dependent Hartree-Fock method for quantum chemical calculations}, issn = {0021-9606}, year = {2005}, abstract = {We apply the multiconfiguration time-dependent Hartree-Fock method to electronic structure calculations and show that quantum chemical information can be obtained with this explicitly time-dependent approach. Different equations of motion are discussed, as well as the numerical cost. The two-electron integrals are calculated using a natural potential expansion, of which we describe the convergence behavior in detail}, language = {en} } @article{SchwarzeDoscheFlehretal.2010, author = {Schwarze, Thomas and Dosche, Carsten and Flehr, Roman and Klamroth, Tillmann and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Saalfrank, Peter and Cleve, Ernst and Buschmann, Hans-J{\"u}rgen and Holdt, Hans-J{\"u}rgen}, title = {Combination of a CT modulated PET and an intramolecular excimer formation to quantify PdCl2 by large fluorescence enhancement}, issn = {1359-7345}, year = {2010}, language = {en} } @article{SchwarzeMuellerDoscheetal.2007, author = {Schwarze, Thomas and Mueller, Holger and Dosche, Carsten and Klamroth, Tillmann and Mickler, Wulfhard and Kelling, Alexandra}, title = {Luminescence detection of open-shell transition-metal ions by photoinduced electron transfer controlled by internal charge transfer of a receptor}, doi = {10.1002/anie.200603992}, year = {2007}, language = {en} } @article{ZenichowskiNacciFoelschetal.2012, author = {Zenichowski, Karl and Nacci, Ch and F{\"o}lsch, S. and Dokic, Jadranka and Klamroth, Tillmann and Saalfrank, Peter}, title = {STM-switching of organic molecules on semiconductor surfaces: an above threshold density matrix model for 1,5 cyclooctadiene on Si(100)}, series = {Journal of physics : Condensed matter}, volume = {24}, journal = {Journal of physics : Condensed matter}, number = {39}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0953-8984}, doi = {10.1088/0953-8984/24/39/394009}, pages = {11}, year = {2012}, abstract = {The scanning tunnelling microscope (STM)-induced switching of a single cyclooctadiene molecule between two stable conformations chemisorbed on a Si(100) surface is investigated using an above threshold model including a neutral ground state and an ionic excited state potential. Switching was recently achieved experimentally with an STM operated at cryogenic temperatures (Nacci et al 2008 Phys. Rev. B 77 121405(R)) and rationalized by a below threshold model using just a single potential energy surface (Nacci et al 2009 Nano Lett. 9 2997). In the present paper, we show that experimental key findings on the inelastic electron tunnelling (IET) switching can also be rationalized using an above threshold density matrix model, which includes, in addition to the neutral ground state potential, an anionic or cationic excited potential. We use one and two-dimensional potential energy surfaces. Furthermore, the influence of two key parameters of the density matrix description, namely the electronic lifetime of the ionic resonance and the vibrational lifetimes, on the ground state potential are discussed.}, language = {en} } @article{BronnerLeyssnerStremlauetal.2012, author = {Bronner, C. and Leyssner, F. and Stremlau, S. and Utecht, Manuel Martin and Saalfrank, Peter and Klamroth, Tillmann and Tegeder, P.}, title = {Electronic structure of a subnanometer wide bottom-up fabricated graphene nanoribbon: End states, band gap, and dispersion}, series = {Physical review : B, Condensed matter and materials physics}, volume = {86}, journal = {Physical review : B, Condensed matter and materials physics}, number = {8}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.86.085444}, pages = {5}, year = {2012}, abstract = {Angle-resolved two-photon photoemission and high-resolution electron energy loss spectroscopy are employed to derive the electronic structure of a subnanometer atomically precise quasi-one-dimensional graphene nanoribbon (GNR) on Au(111). We resolved occupied and unoccupied electronic bands including their dispersion and determined the band gap, which possesses an unexpectedly large value of 5.1 eV. Supported by density functional theory calculations for the idealized infinite polymer and finite size oligomers, an unoccupied nondispersive electronic state with an energetic position in the middle of the band gap of the GNR could be identified. This state resides at both ends of the ribbon (end state) and is only found in the finite sized systems, i.e., the oligomers.}, language = {en} } @article{FuechselTremblayKlamrothetal.2012, author = {F{\"u}chsel, Gernot and Tremblay, Jean Christophe and Klamroth, Tillmann and Saalfrank, Peter and Frischkorn, C.}, title = {Concept of a single temperature for highly nonequilibrium laser-induced hydrogen desorption from a ruthenium surface}, series = {Physical review letters}, volume = {109}, journal = {Physical review letters}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.109.098303}, pages = {5}, year = {2012}, abstract = {Laser-induced condensed phase reactions are often interpreted as nonequilibrium phenomena that go beyond conventional thermodynamics. Here, we show by Langevin dynamics and for the example of femtosecond-laser desorption of hydrogen from a ruthenium surface that light adsorbates thermalize rapidly due to ultrafast energy redistribution after laser excitation. Despite the complex reaction mechanism involving hot electrons in the surface region, all desorption product properties are characterized by equilibrium distributions associated with a single, unique temperature. This represents an example of ultrahot chemistry on the subpicosecond time scale.}, language = {en} } @article{BronnerUtechtHaaseetal.2014, author = {Bronner, Christopher and Utecht, Manuel Martin and Haase, Anton and Saalfrank, Peter and Klamroth, Tillmann and Tegeder, Petra}, title = {Electronic structure changes during the surface-assisted formation of a graphene nanoribbon}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {140}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4858855}, pages = {7}, year = {2014}, abstract = {High conductivity and a tunability of the band gap make quasi-one-dimensional graphene nanoribbons (GNRs) highly interesting materials for the use in field effect transistors. Especially bottom-up fabricated GNRs possess well-defined edges which is important for the electronic structure and accordingly the band gap. In this study we investigate the formation of a sub-nanometer wide armchair GNR generated on a Au(111) surface. The on-surface synthesis is thermally activated and involves an intermediate non-aromatic polymer in which the molecular precursor forms polyanthrylene chains. Employing angle-resolved two-photon photoemission in combination with density functional theory calculations we find that the polymer exhibits two dispersing states which we attribute to the valence and the conduction band, respectively. While the band gap of the non-aromatic polymer obtained in this way is relatively large, namely 5.25 +/- 0.06 eV, the gap of the corresponding aromatic GNR is strongly reduced which we attribute to the different degree of electron delocalization in the two systems.}, language = {en} }