Volume 129, Issue 10, 14 September 2008
Index of content:
129(2008); http://dx.doi.org/10.1063/1.2976008View Description Hide Description
Understanding dissipative and decohering processes is fundamental to the study of quantum systems. An accurate and generic method for investigating these processes is to simulate both the system and environment, which, however, is computationally very demanding. We develop a novel approach to constructing finite representations of the environment based on the influence of different frequency scales on the system’s dynamics. As an illustration, we analyze a solvable model of an optical mode decaying into a reservoir. The influence of the environment modes is constant for small frequencies, but drops off rapidly for large frequencies, allowing for a very sparse representation at high frequencies that gives a significant computational speedup in simulating the environment. This approach provides a general framework for simulating open quantum systems.
Heterodyne-detected electronic sum frequency generation: “Up” versus “down” alignment of interfacial molecules129(2008); http://dx.doi.org/10.1063/1.2981179View Description Hide Description
Heterodyne-detected electronic sum frequency generation (HD-ESFG) spectroscopy is newly developed to obtain complex electronic spectra of interfaces for a simultaneous detection bandwidth broader than 100 nm. HD-ESFG provides linear spectra that have unambiguous information on the “up” versus “down” alignment of interfacial molecules. It is demonstrated for -nitroaniline, a prototypical molecule of nonlinear optical materials, that the up versus down alignment at an air/fused silica interface is critically influenced by a fine modification of the molecule.
Eliminating the domain error in local explicitly correlated second-order Møller–Plesset perturbation theory129(2008); http://dx.doi.org/10.1063/1.2982419View Description Hide Description
A new explicitly correlated local MP2-F12 method is proposed in which the error caused by truncating the virtual orbital space to pair-specific local domains is almost entirely removed. This is achieved by a simple modification of the ansatz for the explicitly correlated wave function, which makes it possible that the explicitly correlated terms correct both for the basis set incompleteness error as well as for the domain error in the LMP2. Benchmark calculations are presented for 21 molecules and 16 chemical reactions. The results demonstrate that the local approximations have hardly any effect on the accuracy of the computed correlation energies and reaction energies, and the LMP2-F12 reaction energies agree within 0.1–0.2 kcal/mol with estimated MP2 basis set limits.
129(2008); http://dx.doi.org/10.1063/1.2977974View Description Hide Description
A theory of coherent resonance energy transfer is developed combining the polaron transformation and a time-local quantum master equation formulation, which is valid for arbitrary spectral densities including common modes. The theory contains inhomogeneous terms accounting for nonequilibrium initial preparation effects and elucidates how quantum coherence and nonequilibrium effects manifest themselves in the coherent energy transfer dynamics beyond the weak resonance coupling limit of the Förster and Dexter (FD) theory. Numerical tests show that quantum coherence can cause significant changes in steady state donor/acceptor populations from those predicted by the FD theory and illustrate delicate cooperation of nonequilibrium and quantum coherenceeffects on the transient population dynamics.