Multiconfiguration perturbation theory with imaginary level shift

Forsberg, Niclas; Malmqvist, Per‐Åke

doi:10.1016/s0009-2614(97)00669-6

Cited by 792 publications

(788 citation statements)

References 13 publications

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“…In order to minimize weakly interacting intruder states, the imaginary level-shift technique with a parameter of 0.2 au was employed. 60 All the CASSCF/CASPT2 calculations were performed by the MOLCAS-7 package of software. 61 On the other hand, from a fundamental point of view, the chemical reactivity of transition metal oxides is strongly influenced by the availability of multiple low-lying electronic states in these species.…”

Section: Methodsmentioning

confidence: 99%

How a Quantum Chemical Topology Analysis Enables Prediction of Electron Density Transfers in Chemical Reactions. The Degenerated Cope Rearrangement of Semibullvalene

González-Navarrete

Andrés

Berski

2012

J. Phys. Chem. Lett.

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A theoretical investigation using density functional theory (DFT) has been carried out in order to understand the molecular mechanism of dihydrogen activation by means of transition metal dioxides MO 2 (M = Ti, Zr and Hf), according to the following reaction: MO 2 + H 2 → MO + H 2 O. B3LYP/6-311++G(2df,2pd)/SDD methodology was employed considering two possible reaction pathways. As first step the hydrogen activation by M=O bonds yields to metal-oxo hydride intermediates O=MH(OH). This process is spontaneous for all metal dioxides, and the stability of the O=MH(OH) species depends on the transition metal center. Subsequently, the reaction mechanism splits into two paths; the first one takes place passing through the M(OH) 2 intermediates yielding to products whereas the second one corresponds to the direct formation of the product complex OM(H 2 O). A two state reactivity mechanism was found for TiO 2 system whereas for ZrO 2 and HfO 2 no spin-crossing processes were observed. This is confirmed by CASSCF/CASPT2 calculations for ZrO 2 that lead to the correct ordering of electronic states not found by DFT. The results obtained in the present paper for MO 2 molecules are consistent with the observed reactivity on surfaces.

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Section: Methodsmentioning

confidence: 99%

How a Quantum Chemical Topology Analysis Enables Prediction of Electron Density Transfers in Chemical Reactions. The Degenerated Cope Rearrangement of Semibullvalene

González-Navarrete

Andrés

Berski

2012

J. Phys. Chem. Lett.

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“…Subsequent energy refinement was done perturbationally with the multi-configurational counterpart of the Møller-Plesset method, denoted as CASPT2, in its single state (SS) version. An imaginary shift of 0.2 68 and an IPEA shift of 0.0 69 were used. 60 states were included in the state-averaging procedure.…”

Section: Computational Detailsmentioning

confidence: 99%

Probing deactivation pathways of DNA nucleobases by two-dimensional electronic spectroscopy: first principles simulations

et al. 2015

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The SOS//QM/MM [Rivalta et al., Int. J. Quant. Chem. 2014, 114, 85.] method consists of an arsenal of computational tools allowing accurate simulation of onedimensional (1D) and bidimensional (2D) electronic spectra of monomeric and dimeric systems with unprecedented details and accuracy. Prominent features like doubly excited local and excimer states, accessible in multi-photon processes, as well as charge-transfer excimer states arise naturally through the fully quantum-mechanical description of the aggregates. In this contribution the SOS//QM/MM approach is extended to simulate time-resolved 2D spectra that can be used to characterize ultrafast excited state relaxation dynamics with atomistic details. We demonstrate how critical structures on the excited state potential energy surface, obtained through state-of-the-art quantum chemical computations, can be used as snapshots of the excited state relaxation dynamics to generate spectral fingerprints for different de-excitation channels. The approach is based on high-level multi-configurational wavefunction methods combined with non-linear response theory and incorporates the effects of the solvent/environment through hybrid quantum mechanics/molecular mechanics (QM/MM) techniques. Specifically, the protocol makes use of the second-order Perturbation theory (CASPT2) on top of Complete Active Space Self Consistent Field (CASSCF) strategy to compute the high-lying excited states that can be accessed in different 2D experimental setups. As an example, the photophysics of the stacked adenine-adenine dimer in a double-stranded DNA is modeled through 2D near-UV spectroscopy.

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“…Large and uniform weights of the zeroth-order wave functions were obtained for all states and distances studied here in the intermediate single state CASPT2 calculations using an imaginary shift of 0.20. 12 The calculations presented here have been performed using the MOLCAS program system. 13 The focus of this paper is on the trends of bond length changes and transition energies with increasing pressure and these trends have been shown to be very slightly affected by spin-orbit on a recent work on Cs 2 NaYCl 6 :U 3+ conducted in our laboratory.…”

Section: Details Of the Calculationsmentioning

confidence: 99%

Relation between high-pressure spectroscopy andfn−1d1excited-state geometry: A comparison between theoretical and experimental results in
Pascual
¹
,
Barandiarán
²
,
Seijo
³

2007
Phys. Rev. B
20
0
4
0
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In this paper, we present the results of ab initio model potential embedded-cluster calculations of Sm 2+ impurities in SrF 2 in order to study the behavior of the electronic transitions of the dopant ion under high hydrostatic pressure. We find that the impurity-ligand bond length shortens upon f → d͑e g ͒ excitation and, as a consequence, the f → d͑e g ͒ transition energy decreases with increasing applied pressure. On the other hand, the bond lengths do not appreciably change upon f → f excitation and the energies of the f → f transitions are almost constant with pressure. These trends are in agreement with spectroscopic measurements under pressure in the title material, which gives credit to the computed bond length changes upon excitation, in contradiction with the widespread assumption of bond length lengthening upon f → d excitations. Spectroscopic experiments under high pressure are shown to be able to provide the sign of bond length changes in electronic transitions, constituting a simpler alternative to difficult excited-state x-ray absorption fine structure experiments.

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Multiconfiguration perturbation theory with imaginary level shift

Cited by 792 publications

References 13 publications

How a Quantum Chemical Topology Analysis Enables Prediction of Electron Density Transfers in Chemical Reactions. The Degenerated Cope Rearrangement of Semibullvalene

How a Quantum Chemical Topology Analysis Enables Prediction of Electron Density Transfers in Chemical Reactions. The Degenerated Cope Rearrangement of Semibullvalene

Probing deactivation pathways of DNA nucleobases by two-dimensional electronic spectroscopy: first principles simulations

Relation between high-pressure spectroscopy andfn−1d1excited-state geometry: A comparison between theoretical and experimental results in
Pascual
¹
,
Barandiarán
²
,
Seijo
³

2007
Phys. Rev. B
20
0
4
0
View full text Add to dashboard Cite

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Multiconfiguration perturbation theory with imaginary level shift

Cited by 792 publications

References 13 publications

How a Quantum Chemical Topology Analysis Enables Prediction of Electron Density Transfers in Chemical Reactions. The Degenerated Cope Rearrangement of Semibullvalene

How a Quantum Chemical Topology Analysis Enables Prediction of Electron Density Transfers in Chemical Reactions. The Degenerated Cope Rearrangement of Semibullvalene

Probing deactivation pathways of DNA nucleobases by two-dimensional electronic spectroscopy: first principles simulations

Relation between high-pressure spectroscopy andfn−1d1excited-state geometry: A comparison between theoretical and experimental results inPascual1, Barandiarán2, Seijo3 2007Phys. Rev. B20040View full textAdd to dashboardCite

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Relation between high-pressure spectroscopy andfn−1d1excited-state geometry: A comparison between theoretical and experimental results in
Pascual
¹
,
Barandiarán
²
,
Seijo
³

2007
Phys. Rev. B
20
0
4
0
View full text Add to dashboard Cite