scholarly journals Generalized Single Excitation Configuration Interaction: An Investigation into the Impact of the Inclusion of Non-Orthogonality on the Calculation of Core-Excited States

2019 ◽  
Author(s):  
Katherine J. Oosterbaan ◽  
Alec F. White ◽  
Diptarka Hait ◽  
Martin Head-Gordon
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Ground States ◽  
Closed Shell ◽  
Open Shell ◽  
Spatial Symmetry ◽  
Exchange Approximation ◽  
Novel Method ◽  
The Impact

<div>In this paper, we investigate different non-orthogonal generalizations of the configuration interaction with single substitutions (CIS) method for the calculation of core-excited states. Fully non-orthogonal CIS (NOCIS) has been described previously for singlets and doublets and this paper reports the extension to triplet molecules. In addition to NOCIS, we present a novel method, 1C-NOCIS(1C-NOCIS), for open-shell molecules which is intermediate between NOCIS and the static exchange approximation (STEX). We explore this hierarchy of spin-pure methods for singlet, doublet, and triplet molecules and conclude that, while NOCIS provides the best results and preserves the spatial symmetry of the wavefunction, 1C-NOCIS retains much of the accuracy of NOCIS at a dramatically reduced cost. For molecules with closed-shell ground states, STEX and 1C-NOCIS are identical.</div>

scholarly journals Generalized Single Excitation Configuration Interaction: An Investigation into the Impact of the Inclusion of Non-Orthogonality on the Calculation of Core-Excited States

2019 ◽  
Author(s):  
Katherine J. Oosterbaan ◽  
Alec F. White ◽  
Diptarka Hait ◽  
Martin Head-Gordon
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Ground States ◽  
Closed Shell ◽  
Open Shell ◽  
Spatial Symmetry ◽  
Exchange Approximation ◽  
Novel Method ◽  
The Impact

<div>In this paper, we investigate different non-orthogonal generalizations of the configuration interaction with single substitutions (CIS) method for the calculation of core-excited states. Fully non-orthogonal CIS (NOCIS) has been described previously for singlets and doublets and this paper reports the extension to triplet molecules. In addition to NOCIS, we present a novel method, 1C-NOCIS(1C-NOCIS), for open-shell molecules which is intermediate between NOCIS and the static exchange approximation (STEX). We explore this hierarchy of spin-pure methods for singlet, doublet, and triplet molecules and conclude that, while NOCIS provides the best results and preserves the spatial symmetry of the wavefunction, 1C-NOCIS retains much of the accuracy of NOCIS at a dramatically reduced cost. For molecules with closed-shell ground states, STEX and 1C-NOCIS are identical.</div>

scholarly journals Photoionisation of Unusual States of Matter: Atomic Ions, Excited States and Open-shell Atoms

1986 ◽  
Vol 39 (5) ◽  
pp. 799
Author(s):  
Steven T Manson ◽  
Samir K Bhattacharya
Keyword(s):  
Excited States ◽  
Periodic Table ◽  
Ground States ◽  
Closed Shell ◽  
Open Shell ◽  
Atomic Ions

Our understanding of the photoionisation of ground states of closed-shell atoms is fairly good. The situation is otherwise for open-shell atoms and for ions and excited states throughout the periodic table. Nevertheless, a number of interesting effects have been predicted theoretically in these unusual states of matter. In this paper, some of these predictions, not yet tested by experiment, shall be discussed, along with their implications.

scholarly journals Hylleraas-Configuration Interaction (Hy-CI) Non-Relativistic Energies for the 3 1S, 4 1S, 5 1S, 6 1S, and 7 1S Excited States of the Beryllium Atom

2020 ◽  
Vol 125 ◽  
Author(s):  
James S. Sims
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Ground States ◽  
Chem Phys ◽  
Isoelectronic Sequence ◽  
Variational Calculations

In a previous work Sims and Hagstrom [J Chem Phys 140,224312(2014)] reported Hylleraas-configuration interaction (Hy-CI) method variational calculations for the 1S ground states of the beryllium isoelectronic sequence with an estimated accuracy of 10 to 20 nanohartrees (nHa). In this work the calculations have been extended to the five higher states of the neutral beryllium atom, 3 1S, 4 1S, 5 1S, 6 1S, and 7 1S. The best non-relativistic energies obtained for these states are -14.4182 4034 6, -14.3700 8789 0, -14.3515 1167 6, -14.3424 0357 8, and -14.3372 6649 96 Ha, respectively. The 6 1S result is superior to the known reference energy for that state, while for the 7 1S state there is no other comparable calculation.

scholarly journals Anti-ohmic Nanoconductors: Myth, Reality and Promise

2021 ◽  
Author(s):  
Ashima Bajaj ◽  
Md. Ehesan Ali
Keyword(s):  
Symmetry Breaking ◽  
Ground State ◽  
Closed Shell ◽  
Open Shell ◽  
Molecular Junctions ◽  
Spatial Symmetry ◽  
New Family ◽  
Diradical Character ◽  
Classical Behavior

The recent accomplishments in the design of molecular nanowires characterised by an increasing conductance with length has embarked the origin of extraordinary new family of molecular junctions referred to as "anti-ohmic" wires. Herein, this highly desirable, non-classical behavior, has been examined for the longer enough molecules exhibiting pronounced diradical character in their ground state within the unrestricted DFT formalism with spin and spatial symmetry breaking. We demonstrate that highly conjugated acenes signals higher resistance in open-shell singlet (OSS) configuration as compared to their closed-shell counterparts. This anomaly has been further put to proof for experimentally certified cumulene wires, which reveals phenomenal modulation in the transport characteristics such that an increasing conductance is observed in closed-shell limit, while higher cumulenes in OSS ground state yields a regular decay of conductance.

scholarly journals Generalized single excitation configuration interaction: an investigation into the impact of the inclusion of non-orthogonality on the calculation of core-excited states

2020 ◽  
Vol 22 (15) ◽  
pp. 8182-8192 ◽  
Author(s):  
Katherine J. Oosterbaan ◽  
Alec F. White ◽  
Diptarka Hait ◽  
Martin Head-Gordon
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
The Impact

In this paper, we investigate different non-orthogonal generalizations of the configuration interaction with single substitutions (CIS) method and their impact on the calculation of core-excited states.

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