scholarly journals Chemical verification of variational second-order density matrix based potential energy surfaces for the N2 isoelectronic series

2010 ◽  
Vol 132 (11) ◽  
pp. 114112 ◽  
Author(s):  
Helen van Aggelen ◽  
Brecht Verstichel ◽  
Patrick Bultinck ◽  
Dimitri Van Neck ◽  
Paul W. Ayers ◽  
...  
Keyword(s):  
Potential Energy ◽  
Density Matrix ◽  
Potential Energy Surfaces ◽  
Second Order ◽  
Isoelectronic Series ◽  
Energy Surfaces

scholarly journals N…C and S…S Interactions in Complexes, Molecules, and Transition Structures HN(CH)SX:SCO, for X = F, Cl, NC, CCH, H, and CN

Molecules ◽  
2019 ◽  
Vol 24 (18) ◽  
pp. 3232
Author(s):  
Janet E. Del Bene ◽  
Ibon Alkorta ◽  
José Elguero
Keyword(s):  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Second Order ◽  
Binding Energies ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Order Dependence ◽  
Transition Structures ◽  
Bond Charge ◽  
Energy Surfaces

Ab initio Møller–Plesset perturbation theory (MP2)/aug’-cc-pVTZ calculations have been carried out in search of complexes, molecules, and transition structures on HN(CH)SX:SCO potential energy surfaces for X = F, Cl, NC, CCH, H, and CN. Equilibrium complexes on these surfaces have C1 symmetry, but these have binding energies that are no more than 0.5 kJ·mol–1 greater than the corresponding Cs complexes which are vibrationally averaged equilibrium complexes. The binding energies of these span a narrow range and are independent of the N–C distance across the tetrel bond, but they exhibit a second-order dependence on the S–S distance across the chalcogen bond. Charge-transfer interactions stabilize all of these complexes. Only the potential energy surfaces HN(CH)SF:SCO and HN(CH)SCl:SCO have bound molecules that have short covalent N–C bonds and significantly shorter S…S chalcogen bonds compared to the complexes. Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) spin-spin coupling constants 1tJ(N–C) for the HN(CH)SX:SCO complexes are small and exhibit no dependence on the N–C distance, while 1cJ(S–S) exhibit a second-order dependence on the S–S distance, increasing as the S–S distance decreases. Coupling constants 1tJ(N–C) and 1cJ(S–S) as a function of the N–C and S–S distances, respectively, in HN(CH)SF:SCO and HN(CH)SCl:SCO increase in the transition structures and then decrease in the molecules. These changes reflect the changing nature of the N…C and S…S bonds in these two systems.

scholarly journals Accuracy of Spin-Component Scaled ADC(2) Excitation Energies and Potential Energy Surfaces

2019 ◽  
Author(s):  
Attila Tajti ◽  
Levente Tulipan ◽  
Péter Szalay
Keyword(s):  
Potential Energy ◽  
Excited States ◽  
Canonical Form ◽  
Potential Energy Surfaces ◽  
Second Order ◽  
Spin Component ◽  
Excitation Energies ◽  
Order Algebraic ◽  
Energy Surfaces

In a recent paper of this Journal (Tajti and Szalay, JCTC 2019, 15, 5523) we have shown that failures of the CC2 method to describe Rydberg excited states, as well as potential energy surfaces of certain valence excited states can be cured by spin-component scaled (SCS) versions SCS-CC2 and SOS-CC2 by a large extent. In this paper, the related and popular Second Order Algebraic Diagrammatic Construction (ADC(2)) method and its SCS variants are inspected with the previously established methodology. The results reflect the similarity of the CC2 and ADC(2) models, showing identical problems in the case of the canonical form and the same improvement when spin-component-scaling is applied.

scholarly journals Accuracy of Spin-Component Scaled ADC(2) Excitation Energies and Potential Energy Surfaces

2019 ◽  
Author(s):  
Attila Tajti ◽  
Levente Tulipan ◽  
Péter Szalay
Keyword(s):  
Potential Energy ◽  
Excited States ◽  
Canonical Form ◽  
Potential Energy Surfaces ◽  
Second Order ◽  
Spin Component ◽  
Excitation Energies ◽  
Order Algebraic ◽  
Energy Surfaces

In a recent paper of this Journal (Tajti and Szalay, JCTC 2019, 15, 5523) we have shown that failures of the CC2 method to describe Rydberg excited states, as well as potential energy surfaces of certain valence excited states can be cured by spin-component scaled (SCS) versions SCS-CC2 and SOS-CC2 by a large extent. In this paper, the related and popular Second Order Algebraic Diagrammatic Construction (ADC(2)) method and its SCS variants are inspected with the previously established methodology. The results reflect the similarity of the CC2 and ADC(2) models, showing identical problems in the case of the canonical form and the same improvement when spin-component-scaling is applied.

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