Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session J26: Focus Session: Non-adiabatic Molecular Dynamics and Control at Conical Intersections II |
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Sponsoring Units: DCP Chair: Michael Ashfold, University of Bristol Room: Colorado Convention Center 205 |
Tuesday, March 6, 2007 11:15AM - 11:51AM |
J26.00001: Aspects of conical intersections: Dynamics, bound states embedded in the continuum and short-lived electronic states Invited Speaker: Conical intersections are omnipresent in polyatomic molecules and their presence gives rise to the most severe breakdown of the Born-Oppenheimer approximation. Several general aspects of conical intersections and of the dynamics through them will be addressed. Particular attention will be paid to the question what happens to the potential energy surfaces if the electronic states are metastable. In addition, it is shown that nuclear dynamics on coupled potential surface can lead to bound states embedded in the continuum. Non-Born-Oppenheimer effects are responsible for the binding of these states. Once the Born-Oppenheimer approximation is introduced, these states at best become resonances which decay via potential tunnelling. The tunnelling is completely suppressed by the coupling between the electronic states. Another important issue which will be touched upon is dynamics in the presence of conical intersections in macrosystems. Here, the number of modes is extremely large and, nevertheless, their impact close to the intersections cannot be neglected. It is shown that effective modes can be derived which reproduce exactly the short-time dynamics of the whole macrosystem at low cost. Numerical examples are given. \newline \newline References: \newline \textit{H. K\"{o}ppel, W. Domcke and L.S. Cederbaum, Adv.Chem.Phys. }\underline {\textit{57}}\textit{, 59 (1984)} \newline \textit{G.A. Worth and L.S. Cederbaum, Annu-Rev.Phys.Chem. }\underline {\textit{55}}\textit{, 127 (2004)} \newline \textit{L.S. Cederbaum, R.S. Friedman, V.M Ryaboy and N. Moiseyev,} \newline \textit{Phys.Rev.Lett. }\underline {\textit{90}}\textit{, 013001 (2003)} \newline \textit{S. Feuerbacher, T. Sommerfeld and L.S. Cederbaum, J.Chem.Phys. }\underline {\textit{120}}\textit{, 3201 (2004)} \newline \textit{L.S. Cederbaum, E. Gindensperger and I. Burghardt, Phys.Rev.Lett. }\underline {\textit{94}}\textit{, 113003 (2005)} [Preview Abstract] |
Tuesday, March 6, 2007 11:51AM - 12:27PM |
J26.00002: Invited Speaker: |
Tuesday, March 6, 2007 12:27PM - 12:39PM |
J26.00003: Semiclassical Description of Non-Adiabatic Dynamics - Part I Nandini Ananth, Charulatha Venkataraman, William Miller Molecular dynamics simulations of systems that involve non-adiabatic transitions has always been challenging as this involves following the coupling between quantum states of the system. The behavior of such systems can best be modeled by making sure that the method used can not only provide a way to incorporate quantum effects, but can also ensures the equivalent treatment of the electronic and nuclear degrees of freedom. We use the classical electron model (Meyer-Miller) to do the latter ; while time evolution using the semiclassical initial value representation (SC-IVR) ensures the inclusion of quantum effects. We are currently studying the viability of this approach with a few test systems. In order to further study the effectiveness of this approach, we are working on several variations of the SC-IVR. For instance, the Forward Backward IVR (FB-IVR) is a variation of the SC-IVR that presents a simplified formulation for correlation functions with a double propagator. The Linearized IVR (LSC-IVR) is yet another variation which results in a more `classical' formulation of the problem. Our observation and results obtained will be presented. [Preview Abstract] |
Tuesday, March 6, 2007 12:39PM - 12:51PM |
J26.00004: Semiclassical description of non-adiabatic dynamics - Part II Charulatha Venkataraman, Nandini Ananth, William Miller Semiclassical IVR is a classical trajectory based method that is used to incorporate quantum effects into classical MD simulations. This, in combination with the classical electron analog model of Meyer and Miller allows us to describe the dynamics on coupled electronic states. The classical electron analog model treats the relevant electronic and nuclear degrees of freedom of a system on the same footing. This achieves dynamical consistency which mixed quantum-classical approaches tend to lack. In joint work with Ananth and Miller, we are studying different IVR approaches to describe non-adiabatic dynamics. One such formulation is ``The Exact Forward-Backward IVR''; this has no other approximation other than the semiclassical description of quantum dynamics. Applications of this approach to various model problems will be presented. [Preview Abstract] |
Tuesday, March 6, 2007 12:51PM - 1:03PM |
J26.00005: Non-adiabatic effects in photoelectron spectroscopy Michael Schuurman, David Yarkony Recent developments in the construction of approximately diabatic second-order Hamiltonians in the vicinity of conical intersections have been employed to study photoelectron spectra of molecules in which nonadiabatic effects are preeminent. Our current approach explicitly includes all non-adiabatic coupling terms through second order, while requiring ab initio data at only (N[int] + 3) or (N[int] + 15) points for two and three-state intersections, respectively, where N[int] is the number of internal coordinates. This scaling allows very accurate wave functions to be used. Since the Hamiltonian is determined at a point of conical intersection, the method is ``self-policing'' in that the ability of the resultant surfaces to reproduce the vicinity of seams of intersection, as well as energy minima and the Franck-Condon region, is easily verified. We will report photoelectron spectra determined from these diabatic representations employing a harmonic oscillator basis and a Lanczos solver algorithm to diagonalize the resultant vibronic Hamiltonian matrices. The results of some initial applications will be discussed, with emphasis on the previously studied five membered heterogeneous ring systems, pyrazolyl (C3H3N2) and pyrrolyl (C4H4N) doublet radicals. These systems are of particular interest since they display low-lying conical intersections adjacent to both the neutral ground state geometries and the Franck-Condon region. [Preview Abstract] |
Tuesday, March 6, 2007 1:03PM - 1:15PM |
J26.00006: Fast and accurate self-interaction-free methods for calculating electronic excitations Martin Head-Gordon Time-dependent density functional theory methods achieve both success and disaster in describing electronic excitations in molecules. Most disasters, such as catastrophic failures for charge-transfer excitations, arise due to self-interaction errors. In this talk, I discuss recent progress on the development of self-interaction free methods for calculating electronic excitations. These methods are based on low-order many-body theory, using auxiliary basis expansions to obtain high computational efficiency. To obtain satisfactory accuracy from non-self-consistent treatment of electron correlations, the use of one or two empirical parameters is explored to scale same-spin and opposite-spin correlations. Using opposite-spin terms only yields a reliable and efficient method which is applicable to molecules in the 100 atom regime, with asymptotically fourth order scaling of computation with molecular size. While calibrated for good performance in the Franck-Condon region, the prospects for extension to conical intersections will be briefly mentioned. [Preview Abstract] |
Tuesday, March 6, 2007 1:15PM - 1:27PM |
J26.00007: Using quantum dynamics simulations to understand motion around a conical intersection Graham Worth Quantum dynamics simulations provide a key support in understanding laser spectroscopy measurements. To do this, a model must first be able to reproduce, or be associated with, an observation. The model can then be analysed to provide a picture at the molecular level. Unfortunately the wavepacket propagation methods used in many quantum dynamics calculations are unable to treat more than a few degrees of freedom: a major bottleneck in photochemical systems where the dynamics is dominated by internal conversion through a conical intersection. The multi-configuration time-dependent Hartree (MCTDH) method is one approach that has been very successful in accurately treating non-adiabatic polyatomic systems. Combined with the vibronic coupling model Hamiltonian we have been able to study in detail the dynamics of a number of molecules as they pass through a conical intersection. Recent work, to be covered in this talk, focuses on the complex photochemistry of benzene, showing how a time-resolved photo-electron spectrum can be calculated and interpreted in terms of the underlying molecular dynamics. [Preview Abstract] |
Tuesday, March 6, 2007 1:27PM - 1:39PM |
J26.00008: Direct dynamics using variational Gaussian wavepackets. Application to the intelligent control of benzene photochemistry Benjamin Lasorne, Michael J. Bearpark, Michael A. Robb, Graham A. Worth The direct dynamics variational multi-configuration Gaussian wavepacket (DD-vMCG) method is based on the multi-configuration time-dependent Hartree (MCTDH) algorithm. It uses a time-dependent basis set of parameterised Gaussian functions, which are coupled so as to variationally provide the best possible representation of the wavepacket. This approach is designed to treat quantum effects in large molecules with on-the-fly calculation of the potential energy surface performed by an interfaced quantum chemistry program. Here, we apply this method to the study of the non-adiabatic photochemistry of benzene. Our aim is to rationalise how the way the wavepacket crosses the $S_{1}$/$S_{0}$ seam may modify the branching ratio Dewar benzene : benzvalene and enhance their production rather than non-radiative decay back to benzene. This study is intended to identify realistic non-radiative decay pathways that lead to alternative photochemical reactivity and to find corresponding targets that can be reached by optimal control experiments. [Preview Abstract] |
Tuesday, March 6, 2007 1:39PM - 1:51PM |
J26.00009: ABSTRACT WITHDRAWN |
Tuesday, March 6, 2007 1:51PM - 2:03PM |
J26.00010: Towards Modeling Coherent Control in Ab Initio Multiple Spawning Methods Todd Martinez Ab initio multiple spawning (AIMS) dynamics has been developed as a method to solve the nuclear and electronic Schr\"{o}dinger equations simultaneously. In this talk, we present new extensions to the AIMS method which allow modeling light absorption with shaped laser pulses for the purposes of achieving coherent control. The new methods are tested on a variety of low-dimensional problems by comparison to numerically exact wavepacket dynamics. [Preview Abstract] |
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