Accuracy Assessment of GW Starting Points for Calculating Molecular Excitation Energies Using the Bethe–Salpeter Formalism

2018 ◽  
Vol 14 (4) ◽  
pp. 2127-2136 ◽  
Author(s):  
Xin Gui ◽  
Christof Holzer ◽  
Wim Klopper
Keyword(s):  
Accuracy Assessment ◽  
Excitation Energies ◽  
Molecular Excitation

Superconducting and Normal State Properties of the A3C60 Compounds

1992 ◽  
Vol 06 (23n24) ◽  
pp. 3967-3991 ◽  
Author(s):  
Károly Holczer
Keyword(s):  
Normal State ◽  
Local Property ◽  
Alkali Atom ◽  
Density Of State ◽  
Excitation Energies ◽  
Cubic Symmetry ◽  
Normal State Properties ◽  
Molecular Excitation ◽  
Superconducting Parameters ◽  
Expected Density

The A 3 C 60 compounds, where A=alkali atom, form fcc -lattices (cryolite structure) and are highly ionic [ A +]3·[ C 60]3−. The C 60 icosahedra are located in sites of local cubic symmetry thereby preserving the degeneracy of the t 1u orbitals, allowing for the formation of a narrow half filled band of a width comparable to or smaller than the various molecular excitation energies. The T c - s of the dozen or so compounds already synthesized span the range from 2–33 K; the variation of T c with pressure and from material to material suggests that the attraction responsible for the Cooper pair formation is a local property of the C 60 molecules, so that variations of the density-of-state ρ(ε F ) at the Fermi level (i.e. bandwidth) determine T c . The values of the superconducting parameters, λ L and ξ o , determined from critical field and µSR measurements, favor a local pairing picture, but are at best only marginally supportive for the expected density-ofstate variations. The so far available 13 C nuclear relaxation, susceptibility and ESR measurements in the normal state manifest several features that are more related to the complex correlated nature of the C 60 molecules than to the freeelectron band effects of the simple lattice they are arranged in.

Impulse approximation neutron scattering from N2

1995 ◽  
Vol 73 (11-12) ◽  
pp. 772-778 ◽  
Author(s):  
R. A. Cowley ◽  
M. P. Zinkin ◽  
R. S. Eccleston ◽  
A. C. Evans ◽  
M. J. Harris
Keyword(s):  
Neutron Scattering ◽  
Inelastic Neutron Scattering ◽  
Impulse Approximation ◽  
Inelastic Neutron ◽  
Vibrational Modes ◽  
Excitation Energies ◽  
Energy Transfers ◽  
Molecular Excitation ◽  
The Individual ◽  
Good Agreement

We present the results of a detailed investigation of the inelastic neutron scattering from diatomic N2, at wave-vector transfers in the range Q = 20–100 Å−1 (1Å = 10−10 m). At intermediate Q, the scattering shows structure arising from the vibrational modes of the molecule, while at large Q the scattering is well described by the impulse approximation for the individual atoms, despite the fact that the corresponding energy transfers are considerably less than the maximum molecular excitation energies. We find good agreement for all Q with a calculation incorporating the internal rotational and vibrational modes of the molecule explicitly.

scholarly journals Quantum equation of motion for computing molecular excitation energies on a noisy quantum processor

2020 ◽  
Vol 2 (4) ◽  
Author(s):  
Pauline J. Ollitrault ◽  
Abhinav Kandala ◽  
Chun-Fu Chen ◽  
Panagiotis Kl. Barkoutsos ◽  
Antonio Mezzacapo ◽  
...  
Keyword(s):  
Equation Of Motion ◽  
Excitation Energies ◽  
Quantum Equation ◽  
Quantum Processor ◽  
Molecular Excitation

scholarly journals Toward an Understanding of Electronic Excitation Energies Beyond the Molecular Orbital Picture

2020 ◽  
Author(s):  
Patrick Kimber ◽  
Felix Plasser
Keyword(s):  
Molecular Orbital ◽  
Electronic Excitation ◽  
Triplet States ◽  
Central Research ◽  
Excitation Energies ◽  
Correlated Electron ◽  
Rough Approximation ◽  
Electron Hole Pair ◽  
Molecular Excitation ◽  
Excitation Processes

<pre><div><div><div><p>Tuning the energies of molecular excited states is a central research theme in modern chemistry with high relevance for optoelectronic applications and chemical synthesis. Whereas frontier orbitals have proven to be an intuitive and simple model in many cases, they can only provide a very rough approximation of the underlying wavefunctions. The purpose of this Perspective is to explore how our qualitative understanding of electronic excitation processes can be promoted beyond the molecular orbital picture by exploiting methods and insights from modern quantum chemistry. For this purpose, the physics of a correlated electron-hole pair is analysed in detail to show the origin of exchange repulsion and a dynamic Coulomb attraction, which determine its energy aside from the orbital energies. Furthermore, we identify and discuss the two additional effects of secondary orbital relaxation and de-excitations. Rules for reconstructing these four contributions from general excited-state computations are presented and their use is exem- plified in three case studies concerned with the relative ordering of the singlet and triplet ππ∗ and nπ∗ states of uracil, the large energetic differences between the first singlet and triplet states of the polyacenes, and the assignment of plasmonic states in octatetraene. Finally, we lay out some general ideas for how the knowledge gained could ultimately lead to new design principles for tuning molecular excitation energies as well as for diagnosing possible shortcomings of commonly used electronic structure methods.</p></div></div></div></pre>

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