Reduced multireference couple cluster method. II. Application to potential energy surfaces of HF, F2, and H2O

1998 ◽  
Vol 108 (2) ◽  
pp. 637-648 ◽  
Author(s):  
Xiangzhu Li ◽  
Josef Paldus
Keyword(s):  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Cluster Method ◽  
Couple Cluster ◽  
Couple Cluster Method ◽  
Energy Surfaces

A Coupled Cluster Study of van der Waals Interactions of the He Atom with CN, NO and O2 Radicals

2004 ◽  
Vol 69 (1) ◽  
pp. 189-212 ◽  
Author(s):  
Juraj Raab ◽  
Andrej Antušek ◽  
Stanislav Biskupič ◽  
Miroslav Urban
Keyword(s):  
Potential Energy ◽  
Interaction Energy ◽  
Potential Energy Surfaces ◽  
Van Der Waals ◽  
Transition States ◽  
Basis Set ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Interaction Energies ◽  
Energy Surfaces

The partially spin-adapted coupled cluster method with the restricted open-shell Hartree- Fock reference was applied to calculations of interaction energies between the helium atom and the three radicals, CN (2Σ), NO (2Π), and O2 (3Sg-). Basis set dependences with medium-augmented correlation consistent basis sets were alleviated by using extrapolations to the basis set limit which were based on aug-cc-pVTZ and aug-cc-pVQZ results. The two-dimensional potential energy surfaces were fitted by exponential and polynomial functions. Minima and transition states were located. Potential energy surfaces are very floppy, especially for HeCN. This complex exhibits the weakest van der Waals interaction, the electronic interaction energy being 92 μEh. Interaction energy in HeNO is 122 μEh, almost the same as was found for HeO2 (124 μEh). Considering zero-point-vibrational corrections, the dissociation energy of HeCN, HeNO, and HeO2 is 4.6, 6.6, and 7.3 cm-1, respectively. This sequence of the magnitude of interaction energies and the structural data for global and local minima and transition states were compared with available literature data. No simple link between the magnitude of intermolecular forces and dipole moments and dipole polarizabilities of CN, NO, and O2 was found. The low-order long-range model based on the induction and dispersion forces is completely useless in the assessment of the sequence of the size of intermolecular interactions of the HeCN, HeNO, and HeO2 complexes.

Resolving the Quadruple Bonding Conundrum in C2 Using Insights Derived from Excited State Potential Energy Surfaces: A Molecular Orbital Perspective

2019 ◽  
Author(s):  
Ishita Bhattacharjee ◽  
Debashree Ghosh ◽  
Ankan Paul
Keyword(s):  
Excited State ◽  
Potential Energy ◽  
Molecular Orbital ◽  
High Spin ◽  
Potential Energy Surfaces ◽  
Valence Bond ◽  
Deep Minimum ◽  
State Potential ◽  
Energy Surfaces ◽  
Mo Theory

The question of quadruple bonding in C<sub>2</sub> has emerged as a hot button issue, with opinions sharply divided between the practitioners of Valence Bond (VB) and Molecular Orbital (MO) theory. Here, we have systematically studied the Potential Energy Curves (PECs) of low lying high spin sigma states of C<sub>2</sub>, N<sub>2</sub> and Be<sub>2</sub> and HC≡CH using several MO based techniques such as CASSCF, RASSCF and MRCI. The analyses of the PECs for the<sup> 2S+1</sup>Σ<sub>g/u</sub> (with 2S+1=1,3,5,7,9) states of C<sub>2</sub> and comparisons with those of relevant dimers and the respective wavefunctions were conducted. We contend that unlike in the case of N<sub>2</sub> and HC≡CH, the presence of a deep minimum in the <sup>7</sup>Σ state of C<sub>2</sub> and CN<sup>+</sup> suggest a latent quadruple bonding nature in these two dimers. Hence, we have struck a reconciliatory note between the MO and VB approaches. The evidence provided by us can be experimentally verified, thus providing the window so that the narrative can move beyond theoretical conjectures.

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