Multiconfigurational Quantum Chemistry

Roos, Björn O.

doi:10.1002/9781119126171

Cited by 170 publications

(180 citation statements)

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“…As an example, we choose to study the zero-field splitting (ZFS) of the spin-free ground state 3 Σ − g of the tellurium dimer Te 2 for which CASSCF-SO reference data are available 102 for both the ZFS and the SO matrix element V between the spin-free 3 Σ − g and 1 Σ + g states. In accordance with the reference work of Rota et al 102 , we employ an all-electron ANO-RCC basis set of TZP quality 103,104 for Te along with the 2nd-order Douglas-Kroll-Hess (DKH2) scalar-relativistic Hamiltonian 105 . The internuclear Te-Te distance of 2.557Å is taken from experiment 106 .…”

Section: Numerical Examples a Closedness Of Mps Wave Function Expmentioning

confidence: 99%

“…We employed all-electron ANO-RCC basis sets of TZP quality 103,104 along with the scalarrelativistic DKH2 Hamiltonian 105 and a Cholesky-decomposition (CD) of the two-electron repulsion integrals as implemented in Molcas 82 (keyword Cholesky in the integral mod- spectively. In all DMRG-SCF calculations, the number renormalized block states m was set to 1024 which is sufficient to yield results of CASSCF quality for the active orbital spaces considered.…”

Section: Numerical Examples a Closedness Of Mps Wave Function Expmentioning

confidence: 99%

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A Nonorthogonal State-Interaction Approach for Matrix Product State Wave Functions

Knecht

Keller

Autschbach

et al. 2016

J. Chem. Theory Comput.

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We present a state-interaction approach for matrix product state (MPS) wave functions in a nonorthogonal molecular orbital basis. Our approach allows us to calculate for example transition and spin-orbit coupling matrix elements between arbitrary electronic states provided that they share the same one-electron basis functions and active orbital space, respectively. The key element is the transformation of the MPS wave functions of different states from a nonorthogonal to a biorthonormal molecular orbital basis representation exploiting a sequence of non-unitary transformations following a proposal by Malmqvist (Int. J. Quantum Chem. 30, 479 (1986)). This is well-known for traditional wave-function parametrizations but has not yet been exploited for MPS wave functions.

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Section: Numerical Examples a Closedness Of Mps Wave Function Expmentioning

confidence: 99%

Section: Numerical Examples a Closedness Of Mps Wave Function Expmentioning

confidence: 99%

A Nonorthogonal State-Interaction Approach for Matrix Product State Wave Functions

Knecht

Keller

Autschbach

et al. 2016

J. Chem. Theory Comput.

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“…Geometry optimizations of the stationary points and minimum energy path (MEP) and intrinsic reaction coordinate (IRC) searches were carried out by employing the complete-active-space self-consistent field (CASSCF) method 49 in conjunction with the atomic natural orbital (ANO-RCC) 50 (hereafter ANO-RCC-VTZP). 51 As it was proved in the 1,2-dioxetane study, 21 increasing the size of the basis set to even larger basis sets does not change the qualitative and quantitative aspects of the chemical process, therefore we confined our calculations by using the ANO-RCC triple-ζ quality basis set.…”

Section: Computational Detailsmentioning

confidence: 99%

Theoretical study of the dark photochemistry of 1,3-butadiene via the chemiexcitation of Dewar dioxetane

Farahani

Lundberg

Lindh

et al. 2015

Phys. Chem. Chem. Phys.

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Excited-state chemistry is usually ascribed to photo-induced processes, such as fluorescence, phosphorescence, and photochemistry, or to bio-and chemiluminescence, in which light emission is originated by a chemical reaction. A third class of excited-state chemistry, however, is possible that promotes photochemical phenomena by chemienergizing certain chemical groups without light -chemiexcitation. By studying Dewar dioxetane, which can be viewed as the combination of 1,2-dioxetane and 1,3-butadiene, we show here how the isomerization * To whom correspondence should be addressed † Uppsala ‡ València ¶ UC 3 1 channel that characterizes the photo-induced chemistry of 1,3-butadiene can be reached at a later stage after the thermal decomposition of the dioxetane moiety. Multi-reference multiconfigurational quantum chemistry methods and accurate reaction-path computational strategies were used to determine the reaction coordinate that first decomposes the dioxetane, next transfers non-adiabatically the state from the ground to the excited state, and finally brings the system into the photochemical channel of the 1,3-butadiene group. With the present study, we open a new area of research within computational photochemistry to study chemically-induced excited-state chemistry that is difficult to tackle experimentally due to the short-lived character of the species involved in the process. The findings shall be of relevance to unveil "dark" photochemistry mechanisms which might operate in biological systems in conditions of lack of light to allow reactions that are typical of photo-induced phenomena.

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“…Multiconfigurational methods are usually the preferred choice, particularly the complete active space self-consistent field (CASSCF) [42] and its second-order perturbation theory extension (CASPT2) [43]. These methods offer an even-footing treatment for all ground and excited-states partaking in the photo-process and are thus expected to properly represent the intricate PEHs and their minima/crossings [44][45][46][47][48]. These not only provide the PEHs for mechanistic purposes, but can also yield excited state absorptions [49,50], cationic energies [41], and other related observables with direct experimental counterparts [51,52].…”

Section: Introductionmentioning

confidence: 99%

Assessment of the Potential Energy Hypersurfaces in Thymine within Multiconfigurational Theory: CASSCF vs. CASPT2

et al. 2016

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Abstract:The present study provides new insights into the topography of the potential energy hypersurfaces (PEHs) of the thymine nucleobase in order to rationalize its main ultrafast photochemical decay paths by employing two methodologies based on the complete active space self-consistent field (CASSCF) and the complete active space second-order perturbation theory (CASPT2) methods: (i) CASSCF optimized structures and energies corrected with the CASPT2 method at the CASSCF geometries and (ii) CASPT2 optimized geometries and energies. A direct comparison between these strategies is drawn, yielding qualitatively similar results within a static framework. A number of analyses are performed to assess the accuracy of these different computational strategies under study based on a variety of numerical thresholds and optimization methods. Several basis sets and active spaces have also been calibrated to understand to what extent they can influence the resulting geometries and subsequent interpretation of the photochemical decay channels. The study shows small discrepancies between CASSCF and CASPT2 PEHs, displaying a shallow planar or twisted 1 (ππ*) minimum, respectively, and thus featuring a qualitatively similar scenario for supporting the ultrafast bi-exponential deactivation registered in thymine upon UV-light exposure. A deeper knowledge of the PEHs at different levels of theory provides useful insight into its correct characterization and subsequent interpretation of the experimental observations. The discrepancies displayed by the different methods studied here are then discussed and framed within their potential consequences in on-the-fly non-adiabatic molecular dynamics simulations, where qualitatively diverse outcomes are expected.

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Multiconfigurational Quantum Chemistry

Cited by 170 publications

References 58 publications

A Nonorthogonal State-Interaction Approach for Matrix Product State Wave Functions

A Nonorthogonal State-Interaction Approach for Matrix Product State Wave Functions

Theoretical study of the dark photochemistry of 1,3-butadiene via the chemiexcitation of Dewar dioxetane

Assessment of the Potential Energy Hypersurfaces in Thymine within Multiconfigurational Theory: CASSCF vs. CASPT2

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