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- Fülscher, Markus P, et al.
(författare)
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Quasi diabatic CASSCF state functions
- 2002
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Ingår i: MOLECULAR PHYSICS. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 100:6, s. 903-909
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Konferensbidrag (refereegranskat)abstract
- A new method to determine quasi diabatic (QD) CASSCF states is presented. The adiabatic states are subjected to a unitary transformation resulting from diagonalization of a state-selection operator. The latter is constructed from the overlap of the adiabatic states with a suitable set of reference states. The multi-state (MS) CASPT2 method is used to account for the dynamical correlation effects in an approach where the QD-CASSCF wave functions are used as reference states. The procedure is applied to avoided crossings in excited states of BeH, LiO and ozone. The advantages of the proposed formulation are discussed.
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- González-Luque, R, et al.
(författare)
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A theoretical analysis of the excited states in 2-benzoylthiophene.
- 2003
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Ingår i: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 101:13, s. 1977-1982
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Tidskriftsartikel (refereegranskat)abstract
- The lower excited states of 2-benzoylthiophene have been studied using ab initio quantum chemical methods based on multiconfigurational wave functions. Six singlet and six triplet excited states have been characterized. The geometry has been optimized for the two lowest triplet states, which are responsible for the photoreactivity of the chromophore in the photosensitizing drug tiaprofenic acid. The T1(π → π*) and T2(n → π*) states have been found to be close in energy with the π → π* state slightly lower. The excited states have been characterized using density difference and spin density plots. The different photochemical behaviour of the two triplet states can be rationalized from the theoretical data.
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- Gonzalez-Luque, R, et al.
(författare)
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Theoretical characterization of the absorption spectra of phenanthrene and its radical cation
- 2003
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Ingår i: Theoretical Chemistry Accounts. - : Springer Science and Business Media LLC. - 1432-881X. ; 110:3, s. 224-232
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Tidskriftsartikel (refereegranskat)abstract
- The vertical absorption spectra of phenanthrene and its radical cation have been studied theoretically by means of a multiconfigurational second-order perturbation approach. Singlet-singlet transition energies and oscillator strengths, and singlet-triplet excitation energies have been studied in the absorption spectrum of phenanthrene up to 6 eV. The absorption spectrum of the phenanthrene radical cation has been computed up to 3.4 eV. The results obtained confirm previous assignments and also lead to new interpretations of the main features of the spectra of these systems.
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- Roos, Björn, et al.
(författare)
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Theoretical characterization of the lowest-energy absorption band of pyrrole
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 116:17, s. 7526-7536
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Tidskriftsartikel (refereegranskat)abstract
- The lowest-energy band of the electronic spectrum of pyrrole has been studied with vibrational resolution by using multiconfigurational second-order perturbation theory (CASPT2) and its multistate extension (MS-CASPT2) in conjunction with large atomic natural orbital-type basis sets including Rydberg functions. The obtained results provide a consistent picture of the recorded spectrum in the energy region 5.5-6.5 eV and confirm that the bulk of the intensity of the band arises from a pipi(*) intravalence transition, in contradiction to recent theoretical claims. Computed band origins for the 3s,3p Rydberg electronic transitions are in agreement with the available experimental data, although new assignments are suggested. As illustrated in the paper, the proper treatment of the valence-Rydberg mixing is particularly challenging for ab initio methodologies and can be seen as the main source of deviation among the recent theoretical results as regards the position of the low-lying valence excited states of pyrrole. (C) 2002 American Institute of Physics.
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- Serrano-Andres, L, et al.
(författare)
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Electronic excited states of conjugated cyclic ketones and thioketones: A theoretical study
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 117:4, s. 1649-1659
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Tidskriftsartikel (refereegranskat)abstract
- Absorption spectra of a series of cyclic conjugated ketones and thioketones have been computed at the multiconfigurational second-order multistate perturbation level of theory, the CASSCF/MS-CASPT2 method. Excitation energies, transition dipole moments, oscillator strengths, and static dipole moments are reported and discussed for excited states with energies lower than approximate to7-8 eV. The main bands of the spectra have been assigned and characterized in most cases for the first time. The spectroscopy of the different systems is compared in detail. Thioketones in particular have low-energy and intense pipi* transitions which suggest corresponding enhanced nonlinear molecular optical properties. Additionally, some of the methods used to estimate these properties from spectroscopic data have been considered in order to analyze the main contributions to the nonlinear optical properties. (C) 2002 American Institute of Physics.
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