High-level multireference methods in the quantum-chemistry program system COLUMBUS: Analytic MR-CISD and MR-AQCC gradients and MR-AQCC-LRT for excited states, GUGA spin–orbit CI and parallel CI density

Lischka, Hans; Shepard, Ron; Pitzer, Russell M.; Shavitt, Isaiah; Dallos, Michal; Müller, Thomas; Szalay, Péter G.; Seth, Michael; Kedziora, Gary S.; Yabushita, Satoshi; Zhang, Zhiyong

doi:10.1039/b008063m

Cited by 413 publications

(324 citation statements)

References 49 publications

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“…From the point of view of the electronic subsystem, the computation of excited-state electronic wave functions and energies usually requires an open-shell formalism and expanded basis sets, and a consistent treatment of the active space is required in configuration interaction calculations. [3][4][5][6][7][8] Furthermore, computing the couplings between the electronic states requires specialized methods, and the electronic couplings are singular, rapidly varying, high-dimensional vectors. From the point of view of the nuclear subsystem, the treatment is complicated by the need to consider a different potential energy surface for each electronic state and transitions between these surfaces.…”

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confidence: 99%

Introductory lecture: Nonadiabatic effects in chemical dynamics

et al. 2004

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Recent progress in the theoretical treatment of electronically nonadiabatic processes is discussed. First we discuss the generalized Born-Oppenheimer approximation, which identifies a subset of strongly coupled states, and the relative advantages and disadvantages of adiabatic and diabatic representations of the coupled surfaces and their interactions are considered. Ab initio diabatic representations that do not require tracking geometric phases or calculating singular nonadiabatic nuclear momentum coupling will be presented as one promising approach for characterizing the coupled electronic states of polyatomic photochemical systems. Such representations can be accomplished by methods based on functionals of the adiabatic electronic density matrix and the identification of reference orbitals for use in an overlap criterion. Next, four approaches to calculating or modeling electronically nonadiabatic dynamics are discussed: (1) accurate quantum mechanical scattering calculations, (2) approximate wave packet methods, (3) surface hopping, and (4) self-consistent-potential semiclassical approaches. The last two of these are particularly useful for polyatomic photochemistry, and recent refinements of these approaches will be discussed. For example, considerable progress has been achieved in making the surface hopping method more applicable to the study of systems with weakly coupled electronic states. This includes introducing uncertainty principle considerations to alleviate the problem of classically forbidden surface hops and the development of an efficient sampling algorithm for low-probability events. A topic whose central importance in a number of quantum mechanical fields is becoming more widely appreciated is the introduction of decoherence into the quantal degrees of freedom to account for the effect of the classical treatment on the other degrees of freedom, and we discuss how the introduction of such decoherence into a self-consistent-potential approximation leads to a reasonably accurate but very practical trajectory method for electronically nonadiabatic processes. Finally, the performances of several dynamical methods for Landau-Zener-type and Rosen-Zener-Demkov-type reactive scattering problems are compared.

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confidence: 99%

Introductory lecture: Nonadiabatic effects in chemical dynamics

et al. 2004

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“…[52][53][54]59 For CASSCF calculations, the COLUMBUS V5.9 (ref. [60][61][62][63] program package was employed.…”

Section: Theoretical Methodsmentioning

confidence: 99%

“…S12 in the ESI †). Since CC2 is known to poorly treat excited states with doubly excited character 64 and the second excited state of C 5 H 6 is known to have a multiconfigurational character with considerable contribution of a LUMO ' HOMO double excitation, the CC2 results are re-evaluated by recalculating the same interpolated path for C 5 Cl 6 employing SA-4-CASSCF(6,5)/6-31G* [60][61][62][63] (see Fig. S11 and a description of the employed CAS in the ESI †).…”

Section: Theoretical Investigation Of Generation and Character Of Ct mentioning

confidence: 99%

Ultrafast photoinduced dynamics of halogenated cyclopentadienes: observation of geminate charge-transfer complexes in solution

Wolf

Schalk

Radloff

et al. 2013

Phys. Chem. Chem. Phys.

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aThe photoinduced dynamics of the fully halogenated cyclopentadienes C 5 Cl 6 and C 5 Br 6 have been investigated in solution and gas phase by femtosecond time-resolved spectroscopy. Both in solution and in gas phase, homolytic dissociation into a halogen radical and a C 5 X 5 (X = Cl, Br) radical was observed.In liquid phase, solvent-dependent formation of charge transfer complexes between geminate radicals was observed for the first time. These complexes were found to be surprisingly stable and offered the opportunity to follow the dynamics of specific radical pairs. In the case of C 5 Cl 6 in trichloroethanol, a reaction of the chlorine radical with molecules from the solvent cage was observed.

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“…The calculations reported here were conducted using the computational packages COLUMBUS [27] and GAMESS [28]. Visualization was rendered with MACMOLPLT [29] and MOLDEN [30].…”

Section: Calculationsmentioning

confidence: 99%

Strong-Field Molecular Ionization from Multiple Orbitals

et al. 2011

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We demonstrate strong-field ionization from multiple orbitals of excited-state uracil molecules. The molecules are excited to the first bright state by an ultrafast laser pulse in the deep ultraviolet and then ionized with a strong-field laser pulse in the near infrared during ultrafast relaxation back down to the ground state. We measure time-and angle-dependent ion yields for multiple fragments created by strongfield ionization, and interpret the temporally and angularly resolved yields via ab initio electronic structure calculations. We find that the angular distribution for the electron removed from the lowest unoccupied molecular orbital follows the symmetry of the molecular orbital, whereas ionization of the molecule by removing electrons from deeper bound orbitals is more complicated.

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High-level multireference methods in the quantum-chemistry program system COLUMBUS: Analytic MR-CISD and MR-AQCC gradients and MR-AQCC-LRT for excited states, GUGA spin–orbit CI and parallel CI density

Cited by 413 publications

References 49 publications

Introductory lecture: Nonadiabatic effects in chemical dynamics

Introductory lecture: Nonadiabatic effects in chemical dynamics

Ultrafast photoinduced dynamics of halogenated cyclopentadienes: observation of geminate charge-transfer complexes in solution

Strong-Field Molecular Ionization from Multiple Orbitals

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