Biomedical subjects

Irene Burghardt

Publications and source records attributed to Irene Burghardt.

7 recordsLinked to original sources

PubMed2006

Short-time dynamics through conical intersections in macrosystems. I. Theory: effective-mode formulation.

The short-time dynamics through a conical intersection of a macrosystem comprising a large number of nuclear degrees of freedom (modes) is investigated. The macrosystem is decomposed into a "system" part carrying a limited number of modes, and an "environment" part. An orthogonal transformation in the environment's space is introduced, as a result of which a subset of three effective modes can be identified which couple directly to the electronic subsystem. Together with the system's modes, these govern the short-time dynamics of the overall macrosystem. The remaining environmental modes couple, in turn, to the effective modes and become relevant at longer times. In this paper, we present the derivation of the effective Hamiltonian, first introduced by Cederbaum et al. [Phys. Rev. Lett. 94, 113003 (2005)], and analyze its properties in some detail. Several special cases and topological aspects are discussed.

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PubMed2006

Short-time dynamics through conical intersections in macrosystems. II. Applications.

We present several numerical applications based upon the effective-mode formulation for the short-time dynamics through conical intersections in macrosystems, as detailed in the preceding paper and first proposed by Cederbaum et al. [Phys. Rev. Lett. 94, 113003 (2005)]. The macrosystem, containing a vast number of nuclear degrees of freedom (modes), is decomposed into a system part and an environment part. Only three effective environmental modes are needed-together with the system's modes-to accurately calculate the low resolution spectra and the short-time dynamics of the entire macrosystem. For the systems discussed here, results are compared to those of a full quantum wave-packet propagation. Some rules are extracted to provide general tendencies; these rules allow one to understand and predict the dynamical properties in more general situations where the exact quantum dynamics of the macrosystem is out of reach.

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PubMed2005

Impact of sulfur vs oxygen on the low-lying excited states of trans-p-coumaric acid and trans-p-coumaric thio acid.

The low-lying excited singlet states of trans-p-coumaric acid (CA) and trans-p-coumaric thio acid (CTA) are investigated in view of characterizing the chromophore of the photoactive yellow protein (PYP), with particular regard to the impact of sulfur on the chromophore's electronic structure. The comparative ab initio study, performed with the highly accurate EOM-CCSD method, shows that the electronic state ordering upon vertical excitation and following in-plane geometry relaxation indeed depends in a very sensitive fashion on the presence of either sulfur or oxygen. The study identifies three relevant excited singlet states, two of which are of pi-pi type while the third state is of n-pi character. The study highlights the role of the latter n-pi state which is shown to be the lowest-lying excited state of CTA at all in-plane geometries under consideration, whereas this is not the case for CA.

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PubMed2005

Short-time dynamics through conical intersections in macrosystems.

The short-time dynamics through a conical intersection of a macrosystem with a vast number of nuclear degrees of freedom (modes) is investigated. For convenience, the macrosystem is decomposed into a system carrying a few modes and a "bath." By transforming the bath modes to new ones, it is shown that only three effective bath modes contribute to the conical intersection. They govern--together with the system's modes--the short-time dynamics of the macrosystem. The remaining bath modes do not directly couple the electronic states and become relevant at longer times. An extensive numerical example is presented.

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PubMed2005

Dynamics of coupled Bohmian and phase-space variables: a moment approach to mixed quantum-classical dynamics.

The theoretical framework of the mixed quantum-classical description given by Burghardt and Parlant [J. Chem. Phys. 120, 3055 (2004)] is detailed. A representation in terms of partial hydrodynamic moments is developed, the dynamics of which is determined by a hierarchy of equations derived from the quantum Liouville equation. Exact equations of motion are obtained, whose quantum-classical approximants are associated with a fluid-dynamical trajectory representation which couples classical variables to quantum hydrodynamic variables. The latter evolve under a generalized hydrodynamic force which also depends upon the classical phase-space variables. The hydrodynamic moment description is shown to be closely connected to mixed quantum-classical phase-space methods.

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PubMed2004

On the dynamics of coupled Bohmian and phase-space variables: a new hybrid quantum-classical approach.

A new approach to the coupling of quantum and classical dynamics is developed, by combining a hydrodynamic, Bohmian description for the quantum subsystem with a Liouville-space description for the classical subsystem. To this end, partial hydrodynamic moments are introduced, the dynamics of which is determined by a hierarchy of equations derived from the quantum Liouville equation. We focus on pure states (wave functions) and introduce a trajectory representation in a hybrid hydrodynamic-Liouvillian phase space. The interleaved trajectory dynamics is guided by a new type of quantum force. For illustration, we consider a pair of bilinearly coupled harmonic oscillators, for which the method is exact.

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PubMed2004

Environmental effects on a conical intersection: a model study.

Excited-state processes at conical intersections (CIs) involving charge transfer phenomena can depend sensitively on the influence of a polar and polarizable environment. We propose here a formulation to describe the chromophore-environment interaction for such situations. In a model study, we focus on an extension of the two-electron two-orbital model by V. Bonacić-Koutecký, J. Koutecký, and J. Michl [Angew. Chem., Int. Ed. Engl., 1987, 26, 170], which yields a diabatic model for the S1-S0 CI in protonated Schiff bases and related systems, and describes the charge properties and charge translocation phenomena associated with this CI. The electrostatic effects of the environment, which are expected to strongly affect the CI topology, are accounted for by a dielectric continuum model. This translates to the image of free energy surfaces for the coupled chromophore-environment system represented by molecular coordinates plus a solvent coordinate. The environment's impact on the location and character of the CI is investigated. The limiting situations of "frozen" and equilibrium solvation effects are examined.

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