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Two-Dimensional Vibrational Spectroscopy of a Dissipative System with the Optimized Mean-Trajectory Approximation.

Alemi M, Loring RF - J Phys Chem B (2014)

Bottom Line: Here we apply this method to an anharmonic chromophore coupled to a harmonic bath.The OMT is shown to well reproduce line shapes and waiting time dynamics in the pure dephasing limit of weak coupling to an off-resonant bath.The OMT is also shown to describe a case where energy transfer is the predominant source of line broadening.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States.

ABSTRACT
The optimized mean-trajectory (OMT) approximation is a semiclassical method for computing vibrational response functions from action-quantized classical trajectories connected by discrete transitions representing radiation-matter interactions. Here we apply this method to an anharmonic chromophore coupled to a harmonic bath. A forward-backward trajectory implementation of the OMT method is described that addresses the numerical challenges of applying the OMT to large systems with disparate frequency scales. The OMT is shown to well reproduce line shapes and waiting time dynamics in the pure dephasing limit of weak coupling to an off-resonant bath. The OMT is also shown to describe a case where energy transfer is the predominant source of line broadening.

No MeSH data available.


Purely absorptive spectra are calculatedfor the parameters inFigure 3 but with quadratic coupling, νLL = 0, νSL = 0.704. Fluctuating frequencyapproximation results are shown in column (a), and OMT approximationresults in column (b). The t2 values arethe same as in Figure 3.
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fig4: Purely absorptive spectra are calculatedfor the parameters inFigure 3 but with quadratic coupling, νLL = 0, νSL = 0.704. Fluctuating frequencyapproximation results are shown in column (a), and OMT approximationresults in column (b). The t2 values arethe same as in Figure 3.

Mentions: In Figure 4, the calculations in Figure 3 are repeated for chromophore–bath couplingthat is quadratic in the chromophore coordinate, νLL = 0, νSL = 0.704. These correspond to the couplingparameters used in Figure 5(a-ii) of ref (69). The OMT results in column (b) of Figure 4 were computed using 35 000 initial conditions,although qualitative features were apparent with a few thousand initialconditions. The waiting time dynamics of the spectra in Figure 4 are qualitatively similar to the dynamics in theLL coupling case. At t2 = 0 peaks showinhomogeneous broadening and become homogeneously broadened as thewaiting time increases. There is greater line broadening for the SLcoupling in Figure 4 than for the LL couplingshown in Figure 3, in agreement with the t2 = 0 calculations in ref (69). The OMT approximationreproduces the line shapes of the fluctuating frequency approximation,including the decay in the peak amplitude as a function of t2 as well as the degree of dephasing relativeto the LL case. Unlike LL coupling terms, anharmonic SL coupling termsdo not enter in determining normal modes. The SL coupling terms areonly incorporated in the OMT approximation through their presencein the full Hamiltonian used to propagate trajectories. The resultsin Figure 4 again demonstrate the capacityof the OMT to reproduce anharmonic effects, even when the action–anglevariables are crudely approximated.


Two-Dimensional Vibrational Spectroscopy of a Dissipative System with the Optimized Mean-Trajectory Approximation.

Alemi M, Loring RF - J Phys Chem B (2014)

Purely absorptive spectra are calculatedfor the parameters inFigure 3 but with quadratic coupling, νLL = 0, νSL = 0.704. Fluctuating frequencyapproximation results are shown in column (a), and OMT approximationresults in column (b). The t2 values arethe same as in Figure 3.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4383732&req=5

fig4: Purely absorptive spectra are calculatedfor the parameters inFigure 3 but with quadratic coupling, νLL = 0, νSL = 0.704. Fluctuating frequencyapproximation results are shown in column (a), and OMT approximationresults in column (b). The t2 values arethe same as in Figure 3.
Mentions: In Figure 4, the calculations in Figure 3 are repeated for chromophore–bath couplingthat is quadratic in the chromophore coordinate, νLL = 0, νSL = 0.704. These correspond to the couplingparameters used in Figure 5(a-ii) of ref (69). The OMT results in column (b) of Figure 4 were computed using 35 000 initial conditions,although qualitative features were apparent with a few thousand initialconditions. The waiting time dynamics of the spectra in Figure 4 are qualitatively similar to the dynamics in theLL coupling case. At t2 = 0 peaks showinhomogeneous broadening and become homogeneously broadened as thewaiting time increases. There is greater line broadening for the SLcoupling in Figure 4 than for the LL couplingshown in Figure 3, in agreement with the t2 = 0 calculations in ref (69). The OMT approximationreproduces the line shapes of the fluctuating frequency approximation,including the decay in the peak amplitude as a function of t2 as well as the degree of dephasing relativeto the LL case. Unlike LL coupling terms, anharmonic SL coupling termsdo not enter in determining normal modes. The SL coupling terms areonly incorporated in the OMT approximation through their presencein the full Hamiltonian used to propagate trajectories. The resultsin Figure 4 again demonstrate the capacityof the OMT to reproduce anharmonic effects, even when the action–anglevariables are crudely approximated.

Bottom Line: Here we apply this method to an anharmonic chromophore coupled to a harmonic bath.The OMT is shown to well reproduce line shapes and waiting time dynamics in the pure dephasing limit of weak coupling to an off-resonant bath.The OMT is also shown to describe a case where energy transfer is the predominant source of line broadening.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States.

ABSTRACT
The optimized mean-trajectory (OMT) approximation is a semiclassical method for computing vibrational response functions from action-quantized classical trajectories connected by discrete transitions representing radiation-matter interactions. Here we apply this method to an anharmonic chromophore coupled to a harmonic bath. A forward-backward trajectory implementation of the OMT method is described that addresses the numerical challenges of applying the OMT to large systems with disparate frequency scales. The OMT is shown to well reproduce line shapes and waiting time dynamics in the pure dephasing limit of weak coupling to an off-resonant bath. The OMT is also shown to describe a case where energy transfer is the predominant source of line broadening.

No MeSH data available.