JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

14 Dec 2012

Volume 137, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 137, 224102 (2012); http://dx.doi.org/10.1063/1.4768244 (8 pages)

Jean-Christophe Denis, Stefan Schumacher, and Ian Galbraith
Enlarge Image | Read More
Page 1 of 3 Pages Return to All Sections Next Page
back to top
RSS Feeds
back to top Perspective

Perspective: Nonadiabatic dynamics theory

John C. Tully

J. Chem. Phys. 137, 22A301 (2012); http://dx.doi.org/10.1063/1.4757762 (7 pages) | Cited 4 times

Online Publication Date: 15 October 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Nonadiabatic dynamics—nuclear motion evolving on multiple potential energy surfaces—has captivated the interest of chemists for decades. Exciting advances in experimentation and theory have combined to greatly enhance our understanding of the rates and pathways of nonadiabatic chemical transformations. Nevertheless, there is a growing urgency for further development of theories that are practical and yet capable of reliable predictions, driven by fields such as solar energy, interstellar and atmospheric chemistry, photochemistry, vision, single molecule electronics, radiation damage, and many more. This Perspective examines the most significant theoretical and computational obstacles to achieving this goal, and suggests some possible strategies that may prove fruitful.
Show PACS
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Db Transition state theory and statistical theories of rate constants
back to top Articles

Surface hopping trajectory simulations with spin-orbit and dynamical couplings

Giovanni Granucci, Maurizio Persico, and Gloria Spighi

J. Chem. Phys. 137, 22A501 (2012); http://dx.doi.org/10.1063/1.4707737 (9 pages) | Cited 2 times

Online Publication Date: 13 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper we consider the inclusion of the spin-orbit interaction in surface hopping molecular dynamics simulations to take into account spin forbidden transitions. Two alternative approaches are examined. The spin-diabatic one makes use of eigenstates of the spin-free electronic Hamiltonian and of math2 and is commonly applied when the spin-orbit coupling is weak. We point out some inconsistencies of this approach, especially important when more than two spin multiplets are coupled. The spin-adiabatic approach is based on the eigenstates of the total electronic Hamiltonian including the spin-orbit coupling. Advantages and drawbacks of both strategies are discussed and illustrated with the help of two model systems.
Show PACS
33.50.Hv Radiationless transitions, quenching
31.15.xv Molecular dynamics and other numerical methods

Electron transfer beyond the static picture: A TDDFT/TD-ZINDO study of a pentacene dimer

Randa Reslan, Kenneth Lopata, Christopher Arntsen, Niranjan Govind, and Daniel Neuhauser

J. Chem. Phys. 137, 22A502 (2012); http://dx.doi.org/10.1063/1.4729047 (6 pages) | Cited 2 times

Online Publication Date: 13 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We use time-dependent density functional theory and time-dependent ZINDO (a semi-empirical method) to study transfer of an extra electron between a pair of pentacene molecules. A measure of the electronic transfer integral is computed in a dynamic picture via the vertical excitation energy from a delocalized anionic ground state. With increasing dimer separation, this dynamical measurement of charge transfer is shown to be significantly larger than the commonly used static approximation (i.e., LUMO+1–LUMO of the neutral dimer, or HOMO–LUMO of the charged dimer), up to an order of magnitude higher at 6 Å. These results offer a word of caution for calculations involving large separations, as in organic photovoltaics, where care must be taken when using a static picture to model charge transfer.
Show PACS
31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)
31.15.E- Density-functional theory
34.70.+e Charge transfer

Critical appraisal of excited state nonadiabatic dynamics simulations of 9H-adenine

Mario Barbatti, Zhenggang Lan, Rachel Crespo-Otero, Jaroslaw J. Szymczak, Hans Lischka, and Walter Thiel

J. Chem. Phys. 137, 22A503 (2012); http://dx.doi.org/10.1063/1.4731649 (14 pages) | Cited 3 times

Online Publication Date: 13 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In spite of the importance of nonadiabatic dynamics simulations for the understanding of ultrafast photo-induced phenomena, simulations based on different methodologies have often led to contradictory results. In this work, we proceed through a comprehensive investigation of on-the-fly surface-hopping simulations of 9H-adenine in the gas phase using different electronic structure theories (ab initio, semi-empirical, and density functional methods). Simulations that employ ab initio and semi-empirical multireference configuration interaction methods predict the experimentally observed ultrafast deactivation of 9H-adenine with similar time scales, however, through different internal conversion channels. Simulations based on time-dependent density functional theory with six different hybrid and range-corrected functionals fail to predict the ultrafast deactivation. The origin of these differences is analyzed by systematic calculations of the relevant reaction pathways, which show that these discrepancies can always be traced back to topographical features of the underlying potential energy surfaces.
Show PACS
33.80.-b Photon interactions with molecules
31.50.Df Potential energy surfaces for excited electronic states
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.15.ee Time-dependent density functional theory

Dynamics of a two-level system coupled to a bath of spins

Haobin Wang and Jiushu Shao

J. Chem. Phys. 137, 22A504 (2012); http://dx.doi.org/10.1063/1.4732808 (10 pages)

Online Publication Date: 13 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The dynamics of a two-level system coupled to a spin bath is investigated via the numerically exact multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) theory. Consistent with the previous work on linear response approximation [N. Makri, J. Phys. Chem. B 103, 2823 (1999)]10.1021/jp9847540, it is demonstrated numerically that this spin-spin-bath model can be mapped onto the well-known spin-boson model if the system-bath coupling strength obeys an appropriate scaling behavior. This linear response mapping, however, may require many bath spin degrees of freedom to represent the practical continuum limit. To clarify the discrepancies resulted from different approximate treatments of this model, the population dynamics of the central two-level system has been investigated near the transition boundary between the coherent and incoherent motions via the ML-MCTDH method. It is found that increasing temperature favors quantum coherence in the nonadiabatic limit of this model, which corroborates the prediction in the previous work [J. Shao and P. Hanggi, Phys. Rev. Lett. 81, 5710 (1998)]10.1103/PhysRevLett.81.5710 based on the non-interacting blip approximation (NIBA). However, the coherent-incoherent boundary obtained by the exact ML-MCTDH simulation is slightly different from the approximate NIBA results. Quantum dynamics in other physical regimes are also discussed.
Show PACS
05.30.Jp Boson systems

Enhanced photoswitching of bridged azobenzene studied by nonadiabatic ab initio simulation

Marcus Böckmann, Nikos L. Doltsinis, and Dominik Marx

J. Chem. Phys. 137, 22A505 (2012); http://dx.doi.org/10.1063/1.4733673 (10 pages) | Cited 2 times

Online Publication Date: 16 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Photoisomerization of a bridged azobenzene derivative (AB-C2) is studied by nonadiabatic ab initio molecular dynamics simulation. The effect of the alkyl bridge linking the two phenyl rings on the Z → E and E → Z photoisomerization pathways and efficiencies is analyzed by detailed comparison to the unbridged parent compound. It is found that the bridge makes E → Z photoisomerization considerably faster and increases its quantum yield, whereas Z → E photoswitching is slightly hindered and has a significantly lower quantum yield although still being ultrafast. The simulations reveal that unsuccessful Z → E photoisomerization attempts can interconvert two pro-enantiomeric forms of Z-AB-C2 via pseudorotation in the excited electronic state.
Show PACS
82.37.Vb Single molecule photochemistry
82.30.Qt Isomerization and rearrangement
Author Select

On-the-fly ab initio molecular dynamics with multiconfigurational Ehrenfest method

Kenichiro Saita and Dmitrii V. Shalashilin

J. Chem. Phys. 137, 22A506 (2012); http://dx.doi.org/10.1063/1.4734313 (8 pages) | Cited 2 times

Online Publication Date: 17 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this article we report the formalism and first implementation of the ab initio multiconfigurational Ehrenfest (AI-MCE) method for simulation of ultrafast nonadiabatic dynamics, which uses the MOLPRO electronic structure program to calculate the potential energy surfaces on the fly. The approach is tested on the benchmark of the excited ππ* state dynamics of ethylene producing the dynamics which agree with previous simulations by ab initio multiple spawning technique. The AI-MCE seems to be robust, stable and efficient.
Show PACS
31.15.A- Ab initio calculations
31.15.xv Molecular dynamics and other numerical methods
31.50.Df Potential energy surfaces for excited electronic states

Nonadiabatic dynamics in open quantum-classical systems: Forward-backward trajectory solution

Chang-Yu Hsieh and Raymond Kapral

J. Chem. Phys. 137, 22A507 (2012); http://dx.doi.org/10.1063/1.4736841 (11 pages) | Cited 5 times

Online Publication Date: 18 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A new approximate solution to the quantum-classical Liouville equation is derived starting from the formal solution of this equation in forward-backward form. The time evolution of a mixed quantum-classical system described by this equation is obtained in a coherent state basis using the mapping representation, which expresses N quantum degrees of freedom in a 2N-dimensional phase space. The solution yields a simple dynamics in which a set of N coherent state coordinates evolves in forward and backward trajectories, while the bath coordinates evolve under the influence of the mean potential that depends on these forward and backward trajectories. It is shown that the solution satisfies the differential form of the quantum-classical Liouville equation exactly. Relations to other mixed quantum-classical and semi-classical schemes are discussed.
Show PACS
05.30.-d Quantum statistical mechanics
02.30.Rz Integral equations
02.60.Nm Integral and integrodifferential equations
03.65.Yz Decoherence; open systems; quantum statistical methods

Theoretical study of charge recombination at the TiO2-electrolyte interface in dye sensitised solar cells

E. Maggio, N. Martsinovich, and A. Troisi

J. Chem. Phys. 137, 22A508 (2012); http://dx.doi.org/10.1063/1.4737101 (8 pages)

Online Publication Date: 19 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The charge recombination reaction from the semiconductor (TiO2) conduction band to electron accepting electrolytes (I2, I2−, I3−) in dye-sensitised solar cells is investigated theoretically. The non-adiabatic theory of electron transfer has been adapted to compute the charge transfer rate measured in different experimental settings (namely with and without external illumination). In both cases we are able to provide an atomic level description of the charge recombination to the electrolyte (CRE), which is in good agreement with the experimental data available. The model employs a detailed density-functional theory (DFT) description of the semiconductor-electrolyte interface and the internal reorganization energy. A continuum dielectric model is used to evaluate the external component of the reorganization energy due to the solvent degrees of freedom. The intrinsic limitations of DFT are kept to a minimum by taking two key energetic parameters (the conduction band edge and the reaction energy) from the experiments. The proposed methodology correctly reproduces (i) the ratio between CRE rate to iodine and triiodide in dark, (ii) the absolute CRE rate to triiodide in dark, and (iii) the absolute CRE rate to I2− under illumination.
Show PACS
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
88.40.H- Solar cells (photovoltaics)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.20.At Surface states, band structure, electron density of states
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.45.Gj Electrolytes
FREE

Decoherence induced by conical intersections: Complexity constrained quantum dynamics of photoexcited pyrazine

Till Westermann and Uwe Manthe

J. Chem. Phys. 137, 22A509 (2012); http://dx.doi.org/10.1063/1.4733676 (11 pages) | Cited 3 times

Online Publication Date: 20 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Decoherence effects induced by conical intersecting potential energy surfaces are studied employing the correlation-based von Neumann (CvN) entropy which provides a measure of the complexity of the underlying wavefunction. As a prototypical example, the S0 → S2 excitation in pyrazine is investigated. The 24-dimensional wavepacket dynamics calculations presented utilize the multi-layer extension of the multi-configurational time-dependent Hartree (MCTDH) approach. An efficient numerical scheme is introduced which facilitates CvN entropy constrained wavepacket propagation within the multi-layer MCTDH approach. In unconstrained multi-layer MCTDH calculations, the CvN-entropy is found to provide a valuable analytical tool for studying the decoherence phenomena present. Investigating the CvN entropy after the S0 → S2 excitation as a function of time, a clear separation of time scales is obtained. It can be related to the different dynamical phenomena present: the initial transfer from the upper (S2) to the lower (S1) adiabatic electronic states rapidly generates vast amounts of CvN-entropy, while the subsequent motion on the anharmonic lower adiabatic potential energy surface only yields a slow increase of the CvN-entropy. Employing CvN-entropy constrained calculations, the sensitivity of the autocorrelation function, the absorption spectrum, and the diabatic electronic population dynamics to complexity constraints is analyzed in detail.
Show PACS
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.50.Df Potential energy surfaces for excited electronic states
31.15.vq Electron correlation calculations for polyatomic molecules
31.15.xr Self-consistent-field methods

Modeling the electron-impact dissociation of methane

Marcin Ziółkowski, Anna Vikár, Maricris Lodriguito Mayes, Ákos Bencsura, György Lendvay, and George C. Schatz

J. Chem. Phys. 137, 22A510 (2012); http://dx.doi.org/10.1063/1.4733706 (11 pages) | Cited 1 time

Online Publication Date: 20 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The product yield of the electron-impact dissociation of methane has been studied with a combination of three theoretical methods: R-matrix theory to determine the electronically inelastic collisional excitation cross sections, high-level electronic structure methods to determine excited states energies and derivative couplings, and trajectory surface hopping (TSH) calculations to determine branching in the dissociation of the methane excited states to give CH3, CH2, and CH. The calculations involve the lowest 24 excited-state potential surfaces of methane, up to the ionization energy. According to the R-matrix calculations, electron impact preferentially produces triplet excited states, especially for electron kinetic energies close to the dissociation threshold. The potential surfaces of excited states are characterized by numerous avoided and real crossings such that the TSH calculations show rapid cascading down to the lowest excited singlet or triplet states, and then slower the dissociation of these lowest states. Product branching for electron-impact dissociation was therefore estimated by combining the electron-impact excitation cross sections with TSH product branching ratios that were obtained from the lowest singlet and triplet states, with the singlet dissociation giving a comparable formation of CH2 and CH3 while triplet dissociation gives CH3 exclusively. The overall branching in electron-impact dissociation is dominated by CH3 over CH2. A small branching yield for CH is also predicted.
Show PACS
34.80.Ht Dissociation and dissociative attachment
34.80.Gs Molecular excitation and ionization
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.80.Be Level crossing and optical pumping
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.X- Alternative approaches

Quasi-diabatic representations of adiabatic potential energy surfaces coupled by conical intersections including bond breaking: A more general construction procedure and an analysis of the diabatic representation

Xiaolei Zhu and David R. Yarkony

J. Chem. Phys. 137, 22A511 (2012); http://dx.doi.org/10.1063/1.4734315 (13 pages) | Cited 5 times

Online Publication Date: 27 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The analytic representation of adiabatic potential energy surfaces and their nonadiabatic interactions is a key component of accurate, fully quantum mechanical descriptions of nonadiabatic dynamics. In this work, we describe extensions of a promising method for representing the nuclear coordinate dependence of the energies, energy gradients, and derivative couplings of Nstate adiabatic electronic states coupled by conical intersections. The description is based on a vibronic coupling model and can describe multichannel dissociation. An important feature of this approach is that it incorporates information about the geometry dependent interstate derivative couplings into the fitting procedure so that the resulting representation is quantifiably quasi diabatic and quasi diabatic in a least squares sense. The reported extensions improve both the rate of convergence and the converged results and will permit the optimization of nonlinear parameters including those parameters that govern the placement of the functions used to describe multichannel dissociation. Numerical results for a coupled quasi-diabatic state representation of the photodissociation process NH3+hv → NH2+H illustrate the potential of the improved algorithm. A second focus in this numerical example is the quasi-diabatic character of the representation which is described and analyzed. Special attention is paid to the immediate vicinity of the conical intersection seam.
Show PACS
82.20.Kh Potential energy surfaces for chemical reactions
82.37.Vb Single molecule photochemistry
31.50.-x Potential energy surfaces
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Mechanisms of bridge-mediated electron transfer: A TDDFT electronic dynamics study

Feizhi Ding, Craig T. Chapman, Wenkel Liang, and Xiaosong Li

J. Chem. Phys. 137, 22A512 (2012); http://dx.doi.org/10.1063/1.4738959 (9 pages) | Cited 1 time

Online Publication Date: 31 July 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a time-dependent density functional theory approach for probing the dynamics of electron transfer on a donor-bridge-acceptor polyene dye scaffold. Two kinds of mechanisms, namely, the superexchange mechanism and the sequential mechanism, may be involved in the electron transfer process. In this work, we have focused on the crossover between these two charge transfer mechanisms on a series of donor-bridge-acceptor polyene dye systems with varying lengths of conjugated bridges. A number of methods and quantities are used to assist in the analysis, including the phase relationship of charge evolution and frequency domain spectra of the time-dependent dipole. Our simulations show that the superexchange mechanism plays a dominant role in the electron transfer from donor to acceptor when the bridge length is small, and the sequential mechanism becomes more important as the polyene bridge is lengthened. Full Ehrenfest dynamics with nuclear motion show that molecular vibrations play a very small role in such ultrafast charge transfer processes.
Show PACS
34.70.+e Charge transfer
31.15.eg Exchange-correlation functionals (in current density functional theory)
33.15.Mt Rotation, vibration, and vibration-rotation constants

How to recover Marcus theory with fewest switches surface hopping: Add just a touch of decoherence

Brian R. Landry and Joseph E. Subotnik

J. Chem. Phys. 137, 22A513 (2012); http://dx.doi.org/10.1063/1.4733675 (13 pages) | Cited 3 times

Online Publication Date: 31 July 2012

Full Text: Read Online (HTML) | Download PDF


See Also: Erratum

Show Abstract
We present a slightly improved version of our augmented fewest switches surface hopping (A-FSSH) algorithm and apply it to the calculation of transition rates between diabatic electronic states within the spin-boson model. We compare A-FSSH rates with (i) Marcus rates from the golden rule, (ii) Tully-style FSSH rates, and (iii) FSSH rates using a simple, intuitive decoherence criterion. We show that unlike FSSH, A-FSSH recovers the correct scaling with diabatic coupling (quadratic in V) as well as the lack of dependence on harmonic frequency ω for small enough values of ω and large enough temperatures.
Show PACS
73.25.+i Surface conductivity and carrier phenomena
05.30.Jp Boson systems
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
72.20.Ee Mobility edges; hopping transport

Surface hopping dynamics using a locally diabatic formalism: Charge transfer in the ethylene dimer cation and excited state dynamics in the 2-pyridone dimer

Felix Plasser, Giovanni Granucci, Jiri Pittner, Mario Barbatti, Maurizio Persico, and Hans Lischka

J. Chem. Phys. 137, 22A514 (2012); http://dx.doi.org/10.1063/1.4738960 (13 pages) | Cited 2 times

Online Publication Date: 1 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this work, the advantages of a locally diabatic propagation of the electronic wave function in surface hopping dynamics proceeding on adiabatic surfaces are presented providing very stable results even in challenging cases of highly peaked nonadiabatic interactions. The method was applied to the simulation of transport phenomena in the stacked ethylene dimer radical cation and the hydrogen bonded 2-pyridone dimer. Systematic tests showed the reliability of the method, in situations where standard methods relying on an adiabatic propagation of the wave function and explicit calculation of the nonadiabatic coupling terms exhibited significant numerical instabilities. Investigations of the ethylene dimer radical cation with an intermolecular distance of 7.0 Å provided a quantitative description of diabatic charge trapping. For the 2-pyidone dimer, a complex dynamics was obtained: a very fast (<10 fs) initial S2/S1 internal conversion; subsequent excitation energy transfers with a characteristic time of 207 fs; and the occurrence of proton coupled electron transfer (PCET) in 26% of the trajectories. The computed characteristic excitation energy transfer time of 207 fs is in satisfactory agreement with the experimental value of 318 fs derived from the vibronic exciton splittings in a monodeuterated 2-pyridone dimer complex. The importance of nonadiabatic coupling for the PCET related to the electron transfer was demonstrated by the dynamics simulations.
Show PACS
72.20.Ee Mobility edges; hopping transport
73.25.+i Surface conductivity and carrier phenomena
71.35.-y Excitons and related phenomena
71.70.Gm Exchange interactions

N(4S /2D)+N2: Accurate ab initio-based DMBE potential energy surfaces and surface-hopping dynamics

B. R. L. Galvão, P. J. S. B. Caridade, and A. J. C. Varandas

J. Chem. Phys. 137, 22A515 (2012); http://dx.doi.org/10.1063/1.4737858 (13 pages) | Cited 3 times

Online Publication Date: 1 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This work gives a full account of the N(4S/2D)+N2(1Σg+) interactions via accurate electronic structure calculations and study of the involved exchange reactions. A 2 × 2 diabatic representation of the potential energy surface is suggested for N3(2A′), which, combined with the two previously reported adiabatic forms for 2A″ and another for 4A″, completes the set of five global potentials required to study the title collisional processes. The trajectory results provide the first N(2D)+N2 rate constants, and allow a comparison with the ones for N(4S)+N2. Nonadiabatic effects are estimated by surface hopping, and the geometrical phase effect assessed by following the trajectories that encircle the crossing seam.
Show PACS
31.15.ae Electronic structure and bonding characteristics
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Evaluation of the importance of spin-orbit couplings in the nonadiabatic quantum dynamics with quantum fidelity and with its efficient “on-the-fly” ab initio semiclassical approximation

Tomáš Zimmermann and Jiří Vaníček

J. Chem. Phys. 137, 22A516 (2012); http://dx.doi.org/10.1063/1.4738878 (8 pages)

Online Publication Date: 1 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We propose to measure the importance of spin-orbit couplings (SOCs) in the nonadiabatic molecular quantum dynamics rigorously with quantum fidelity. To make the criterion practical, quantum fidelity is estimated efficiently with the multiple-surface dephasing representation (MSDR). The MSDR is a semiclassical method that includes nuclear quantum effects through interference of mixed quantum-classical trajectories without the need for the Hessian of potential energy surfaces. Two variants of the MSDR are studied, in which the nuclei are propagated either with the fewest-switches surface hopping or with the locally mean field dynamics. The fidelity criterion and MSDR are first tested on one-dimensional model systems amenable to numerically exact quantum dynamics. Then, the MSDR is combined with “on-the-fly” computed electronic structure to measure the importance of SOCs and nonadiabatic couplings in the photoisomerization dynamics of CH 2 NH 2+ considering 20 electronic states and in the collision of F + H2 considering six electronic states.
Show PACS
31.15.at Molecule transport characteristics; molecular dynamics; electronic structure of polymers
31.15.xv Molecular dynamics and other numerical methods
31.50.-x Potential energy surfaces
34.20.Gj Intermolecular and atom-molecule potentials and forces
82.20.Kh Potential energy surfaces for chemical reactions
82.30.Qt Isomerization and rearrangement

Non-adiabatic molecular dynamics with complex quantum trajectories. I. The diabatic representation

Noa Zamstein and David J. Tannor

J. Chem. Phys. 137, 22A517 (2012); http://dx.doi.org/10.1063/1.4739845 (6 pages) | Cited 2 times

Online Publication Date: 8 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We extend a recently developed quantum trajectory method [Y. Goldfarb, I. Degani, and D. J. Tannor, J. Chem. Phys. 125, 231103 (2006)]10.1063/1.2400851 to treat non-adiabatic transitions. Each trajectory evolves on a single surface according to Newton's laws with complex positions and momenta. The transfer of amplitude between surfaces stems naturally from the equations of motion, without the need for surface hopping. In this paper we derive the equations of motion and show results in the diabatic representation, which is rarely used in trajectory methods for calculating non-adiabatic dynamics. We apply our method to the first two benchmark models introduced by Tully [J. Chem. Phys. 93, 1061 (1990)]10.1063/1.459170. Besides giving the probability branching ratios between the surfaces, the method also allows the reconstruction of the time-dependent wavepacket. Our results are in quantitative agreement with converged quantum mechanical calculations.
Show PACS
31.15.xv Molecular dynamics and other numerical methods
31.50.-x Potential energy surfaces

Non-adiabatic molecular dynamics with complex quantum trajectories. II. The adiabatic representation

Noa Zamstein and David J. Tannor

J. Chem. Phys. 137, 22A518 (2012); http://dx.doi.org/10.1063/1.4739846 (6 pages) | Cited 2 times

Online Publication Date: 8 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a complex quantum trajectory method for treating non-adiabatic dynamics. Each trajectory evolves classically on a single electronic surface but with complex position and momentum. The equations of motion are derived directly from the time-dependent Schrödinger equation, and the population exchange arises naturally from amplitude-transfer terms. In this paper the equations of motion are derived in the adiabatic representation to complement our work in the diabatic representation [N. Zamstein and D. J. Tannor, J. Chem. Phys. 137, 22A517 (2012)]10.1063/1.4739845. We apply our method to two benchmark models introduced by John Tully [J. Chem. Phys. 93, 1061 (1990)]10.1063/1.459170, and get very good agreement with converged quantum-mechanical calculations. Specifically, we show that decoherence (spatial separation of wavepackets on different surfaces) is already contained in the equations of motion and does not require ad hoc augmentation.
Show PACS
34.35.+a Interactions of atoms and molecules with surfaces
03.65.Ge Solutions of wave equations: bound states
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Nonlinear dimensionality reduction for nonadiabatic dynamics: The influence of conical intersection topography on population transfer rates

Aaron M. Virshup, Jiahao Chen, and Todd J. Martínez

J. Chem. Phys. 137, 22A519 (2012); http://dx.doi.org/10.1063/1.4742066 (10 pages) | Cited 4 times

Online Publication Date: 9 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Conical intersections play a critical role in the nonadiabatic relaxation of excited electronic states. However, there are an infinite number of these intersections and it is difficult to predict which are actually relevant. Furthermore, traditional descriptors such as intrinsic reaction coordinates and steepest descent paths often fail to adequately characterize excited state reactions due to their highly nonequilibrium nature. To address these deficiencies in the characterization of excited state mechanisms, we apply a nonlinear dimensionality reduction scheme (diffusion mapping) to generate reaction coordinates directly from ab initio multiple spawning dynamics calculations. As illustrated with various examples of photoisomerization dynamics, excited state reaction pathways can be derived directly from simulation data without any a priori specification of relevant coordinates. Furthermore, diffusion maps also reveal the influence of intersection topography on the efficiency of electronic population transfer, providing further evidence that peaked intersections promote nonadiabatic transitions more effectively than sloped intersections. Our results demonstrate the usefulness of nonlinear dimensionality reduction techniques as powerful tools for elucidating reaction mechanisms beyond the statistical description of processes on ground state potential energy surfaces.
Show PACS
31.15.ae Electronic structure and bonding characteristics
31.50.Df Potential energy surfaces for excited electronic states
82.20.Kh Potential energy surfaces for chemical reactions
82.30.Qt Isomerization and rearrangement

Electron wavepacket dynamics in highly quasi-degenerate coupled electronic states: A theory for chemistry where the notion of adiabatic potential energy surface loses the sense

Takehiro Yonehara and Kazuo Takatsuka

J. Chem. Phys. 137, 22A520 (2012); http://dx.doi.org/10.1063/1.4742155 (13 pages) | Cited 1 time

Online Publication Date: 10 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We develop a theory and the method of its application for chemical dynamics in systems, in which the adiabatic potential energy hyper-surfaces (PES) are densely quasi-degenerate to each other in a wide range of molecular geometry. Such adiabatic electronic states tend to couple each other through strong nonadiabatic interactions. Technically, therefore, it is often extremely hard to accurately single out the individual PES in those systems. Moreover, due to the mutual nonadiabatic couplings that may spread wide in space and due to the energy-time uncertainty relation, the notion of the isolated and well-defined potential energy surface should lose the sense. On the other hand, such dense electronic states should offer a very interesting molecular field in which chemical reactions to proceed in characteristic manners. However, to treat these systems, the standard theoretical framework of chemical reaction dynamics, which starts from the Born-Oppenheimer approximation and ends up with quantum nuclear wavepacket dynamics, is not very useful. We here explore this problem with our developed nonadiabatic electron wavepacket theory, which we call the phase-space averaging and natural branching (PSANB) method [T. Yonehara and K. Takatsuka, J. Chem. Phys. 129, 134109 (2008)]10.1063/1.2987302, or branching-path representation, in which the packets are propagated in time along the non-Born-Oppenheimer branching paths. In this paper, after outlining the basic theory, we examine using a one-dimensional model how well the PSANB method works with such densely quasi-degenerate nonadiabatic systems. To do so, we compare the performance of PSANB with the full quantum mechanical results and those given by the fewest switches surface hopping (FSSH) method, which is known to be one of the most reliable and flexible methods to date. It turns out that the PSANB electron wavepacket approach actually yields very good results with far fewer initial sampling paths. Then we apply the electron wavepacket dynamics in path-branching representation and the so-called semiclassical Ehrenfest theory to a hydrogen molecule embedded in twelve membered boron cluster (B12) in excited states, which are densely quasi-degenerate due to the vacancy in 2p orbitals of boron atom [1s22s22p1]. Bond dissociation of the hydrogen molecule quickly takes place in the cluster and the resultant hydrogen atoms are squeezed out to the surface of the cluster. We further study collision dynamics between H2 and B12, which also gives interesting phenomena. The present study suggests an interesting functionality of the boron clusters.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
31.50.Df Potential energy surfaces for excited electronic states
33.15.Bh General molecular conformation and symmetry; stereochemistry
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Kh Potential energy surfaces for chemical reactions

Density matrix treatment of non-adiabatic photoinduced electron transfer at a semiconductor surface

David A. Micha

J. Chem. Phys. 137, 22A521 (2012); http://dx.doi.org/10.1063/1.4742310 (10 pages) | Cited 2 times

Online Publication Date: 15 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Photoinduced electron transfer at a nanostructured surface leads to localized transitions and involves three different types of non-adiabatic couplings: vertical electronic transitions induced by light absorption emission, coupling of electronic states by the momentum of atomic motions, and their coupling due to interactions with electronic density fluctuations and vibrational motions in the substrate. These phenomena are described in a unified way by a reduced density matrix (RDM) satisfying an equation of motion that contains dissipative rates. The RDM treatment is used here to distinguish non-adiabatic phenomena that are localized from those due to interaction with a medium. The fast decay of localized state populations due to electronic density fluctuations in the medium has been treated within the Lindblad formulation of rates. The formulation is developed introducing vibronic states constructed from electron orbitals available from density functional calculations, and from vibrational states describing local atomic displacements. Related ab initio molecular dynamics calculations have provided diabatic momentum couplings between excited electronic states. This has been done in detail for an indirect photoexcitation mechanism of the surface Ag3Si(111):H, which leads to long lasting electronic charge separation. The resulting coupled density matrix equations are solved numerically to obtain the population of the final charge-separated state as it changes over time, for several values of the diabatic momentum coupling. New insight and unexpected results are presented here which can be understood in terms of photoinduced non-adiabatic transitions involving many vibronic states. It is found that the population of long lasting charge separation states is larger for smaller momentum coupling, and that their population grows faster for smaller coupling.
Show PACS
73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
63.22.Kn Clusters and nanocrystals
68.43.Mn Adsorption kinetics

Symmetry, vibrational energy redistribution and vibronic coupling: The internal conversion processes of cycloketones

Thomas S. Kuhlman, Stephan P. A. Sauer, Theis I. Sølling, and Klaus B. Møller

J. Chem. Phys. 137, 22A522 (2012); http://dx.doi.org/10.1063/1.4742313 (9 pages) | Cited 3 times

Online Publication Date: 15 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper, we discern two basic mechanisms of internal conversion processes; one direct, where immediate activation of coupling modes leads to fast population transfer and one indirect, where internal vibrational energy redistribution leads to equidistribution of energy, i.e., ergodicity, and slower population transfer follows. Using model vibronic coupling Hamiltonians parameterized on the basis of coupled-cluster calculations, we investigate the nature of the Rydberg to valence excited-state internal conversion in two cycloketones, cyclobutanone and cyclopentanone. The two basic mechanisms can amply explain the significantly different time scales for this process in the two molecules, a difference which has also been reported in recent experimental findings [T. S. Kuhlman, T. I. Sølling, and K. B. Møller, ChemPhysChem. 13, 820 (2012)]10.1002/cphc.201100929.
Show PACS
33.20.Tp Vibrational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Modelling vibrational coherence in the primary rhodopsin photoproduct

O. Weingart and M. Garavelli

J. Chem. Phys. 137, 22A523 (2012); http://dx.doi.org/10.1063/1.4742814 (6 pages)

Online Publication Date: 15 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Molecular dynamics simulations of the rhodopsin photoreaction reveal coherent low frequency oscillations in the primary photoproduct (photorhodopsin), with frequencies slightly higher than observed in the experiment. The coherent molecular motions in the batho-precursor can be attributed to the activation of ground state vibrational modes in the hot photo-product, involving out-of-plane deformations of the carbon skeleton. Results are discussed and compared with respect to spectroscopic data and suggested reaction mechanisms.
Show PACS
87.15.R- Reactions and kinetics
02.60.-x Numerical approximation and analysis
82.50.-m Photochemistry
87.15.ap Molecular dynamics simulation

9D nonadiabatic quantum dynamics through a four-state conical intersection: Investigating the homolysis of the O–O bond in anthracene-9,10-endoperoxide

Mariana Assmann, Graham A. Worth, and Leticia González

J. Chem. Phys. 137, 22A524 (2012); http://dx.doi.org/10.1063/1.4742908 (12 pages) | Cited 1 time

Online Publication Date: 15 August 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The excited state dynamics of anthracene-9,10-endoperoxide is investigated using quantum wavepacket dynamics. APO is an aromatic endoperoxide which, upon excitation to S1, shows a cleavage of the oxygen–oxygen bond, leading to rearrangement products. It was shown that the dynamics of the O–O cleavage is modulated by a four-state degeneracy [D. Mollenhauer, I. Corral, and L. González, J. Phys. Chem. Lett. 1, 1036 (2010)]10.1021/jz100196q. The most important mode to describe the O–O cleavage is the opening of the O–O bond. Excitation to higher excited states Sn (n ⩾ 2) leads to the release of singlet molecular oxygen. For this release, the twist of the oxygen atoms around the molecular axis is an important mode. These two degrees of freedom were employed to calculate two-dimensional potential energy surfaces for the four singlet states which become degenerate. Further modes were included in terms of harmonic oscillators. Using the multiconfigurational time-dependent Hartree method, quantum dynamic simulations were performed in up to nine degrees of freedom. Moreover, the nine branching space vectors, which prove the degeneracy to be a four-state conical intersection (4CI), were calculated and included in the wavepacket propagations. The resulting dynamics show that the 4CI is reached very fast (in less than 30 fs after excitation) and the wavepacket distributes over all states. The degree of distribution into the states is very much dependent on which modes are included in the simulation.
Show PACS
33.15.Fm Bond strengths, dissociation energies
31.15.xr Self-consistent-field methods
31.50.Df Potential energy surfaces for excited electronic states
Page 1 of 3 Pages Return to All Sections Next Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close