Diatom–diatom interactions: Building potential energy surfaces and effect of intramolecular vibrations

Carmona‐Novillo, Estela; Bartolomei, Massimiliano; Pérez‐Ríos, Jesús; Campos‐Martínez, José; Hernández, Marta I.

doi:10.1002/qua.22680

Cited by 5 publications

(4 citation statements)

References 33 publications

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“…The vdW-DF-optB86b result [Fig. 9 (b)] for the FM O 2 -O 2 dimer is closer to highest-accuracy quantum chemistry calculations available in the literature for the quintet state of the dimer, which predicts an interaction energy of ∼ 14 meV 34 . The better result may be due to the fact that the optB86b exchange is similar to the exchange employed in the newer vdW-DF-cx 35 , where the exchange functional is constructed to be more consistent with the underlying justification of vdW-DF based on adiabatic connection 17 .…”

Section: Resultssupporting

confidence: 73%

First-principles description of van der Waals bonded spin-polarized systems using the vdW-DF+ U method: Application to solid oxygen at low pressure

2017

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The description of the molecular solid phase of O2, especially its ground-state antiferromagnetic insulating phase, is known to be quite unsatisfactory within the local and semilocal approximations conventionally used in the Kohn-Sham formalism of density functional theory (DFT). The recentlydeveloped van der Waals (vdW) density functionals, vdW-DF, that take into account nonlocal correlations have also shown subpar performance in this regard. The difficulty lies in the subtle balance between the vdW interactions and the exchange coupling between the spin-triplet state of molecules in the molecular crystal. Here, we report that the DFT+U approach used in combination with the vdW-DF performs surprisingly well in this regard, and discuss the reasoning behind this behavior. We also apply this approach to study the recently-reported magnetic field-induced θ phase of solid O2.

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Section: Resultssupporting

confidence: 73%

First-principles description of van der Waals bonded spin-polarized systems using the vdW-DF+ U method: Application to solid oxygen at low pressure

2017

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“…In a sense it is a generalization of the four-term expansion mentioned before to a more accurate nine term representation. Later on, this analysis was extended for the calculation of other terms, 59 where it was demonstrated that 𝑉 202 and 𝑉 404 can be obtained with the same level of precision, in comparison with the isotropic one, starting from the KK conformations. This conclusion was based on a comparison with a very accurate representation of the quintet state, based on calculations at 65 different geometries and involving 29 radial terms 29 obtained from numerical integration over the angular coordinates.…”

Section: Geometries and Spherical Harmonic Expansion Of The Potential...mentioning

confidence: 99%

“…In these studies,[58][59] it was demonstrated that the expressions for the coefficients 𝑉 000 and 𝑉 202 from KK conformations, are those collected in the following equations:…”

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confidence: 99%

An unrestricted approach for the accurate calculation of the interaction potentials of open-shell monomers: The case of O2–O2

Valentín-Rodríguez

Bartolomei

Hernández

et al. 2020

The Journal of Chemical Physics

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The properties of molecular oxygen including its condensed phases continue to be of great relevance for the scientific community. The richness and complexity of their associated properties stem from the fact that it is a very stable diradical. Its open-shell nature leads to low-lying multiplets with total electronic spin 𝑺 = 𝟎, 𝟏, 𝟐 in the case of the dimer, (𝑶 𝟐 ) 𝟐 , and the accurate calculation of their intermolecular potentials represents a challenge to ab initio electronic structure methods. In this work we present intermolecular potentials calculated at a very high level, thus competing with the most accurate restricted potentials obtained to date. This is accomplished by drawing on an analogy between the coupled and uncoupled representations of angular momentum and restricted vs unrestricted methodologies. The 𝑺 = 𝟐 state can be well represented by unrestricted calculations in which the spins of the unpaired electrons are aligned in parallel; however for the state where they are aligned in antiparallel fashion it would seem the total spin is not well defined i.e. the well-known spin contamination problem. We show that its energy corresponds to that of the 𝑺 = 𝟏 state and perform unrestricted coupled cluster calculations for these two states. Then we obtain the 𝑺 = 𝟎 state through the Heisenberg Hamiltonian and show that this is very reliable in the well region of the potentials. We make extensive comparisons with the best restricted potentials (Bartolomei, et al Phys. Chem. Chem. Phys., 10, 1-7, 2008) and with reliable experimental determinations, a very good agreement is globally found.

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“…In the experiments considered here, all molecules must be in their ground vibrational state so that an improved model could consist in obtaining PESs averaged over the ground vibrational state of the monomers. Very recently, 60 vibrational averages of the isotropic ͑f 000 ͒ and the leading anisotropic ͑f 202 ͒ terms were obtained by means of RCCSD͑T͒ calculations of the quintet state for a set of different intramolecular distances ͑Gauss-Hermite quadrature points͒ as well as a reduced set of relative orientations. It was found that the vibrationally averaged terms are just about 1% more attractive ͑in the well region͒ than the rigid rotor counterparts while being slightly more repulsive at shorter range.…”

Section: Concluding Remarks and Perspectivesmentioning

confidence: 99%

Global ab initio potential energy surfaces for the O2(Σ3g−)+O2(Σ3g−) interaction

Bartolomei

Carmona‐Novillo

Hernández

et al. 2010

The Journal of Chemical Physics

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Completely ab initio global potential energy surfaces (PESs) for the singlet and triplet spin multiplicities of rigid O(2)((3)Σ(g)(-))+O(2)((3)Σ(g)(-)) are reported for the first time. They have been obtained by combining an accurate restricted coupled cluster theory with singles, doubles, and perturbative triple excitations [RCCSD(T)] quintet potential [Bartolomei et al., J. Chem. Phys. 128, 214304 (2008)] with complete active space second order perturbation theory (CASPT2) or, alternatively, multireference configuration interaction (MRCI) calculations of the singlet-quintet and triplet-quintet splittings. Spherical harmonic expansions, containing a large number of terms due to the high anisotropy of the interaction, have been built from the ab initio data. The radial coefficients of these expansions are matched at long range distances with analytical functions based on recent ab initio calculations of the electric properties of the monomers [M. Bartolomei, E. Carmona-Novillo, M. I. Hernández, J. Campos-Martínez, and R. Hernández-Lamoneda, J. Comput. Chem. (2010) (in press)]. The singlet and triplet PESs obtained from either RCCSD(T)-CASPT2 or RCCSD(T)-MRCI calculations are quite similar, although quantitative differences appear in specific terms of the expansion. CASPT2 calculations are the ones giving rise to larger splittings and more attractive interactions, particularly in the region of the absolute minima (in the rectangular D(2h) geometry). The new singlet, triplet, and quintet PESs are tested against second virial coefficient B(T) data and, their spherically averaged components, against integral cross sections measured with rotationally hot effusive beams. Both types of multiconfigurational approaches provide quite similar results, which, in turn, are in good agreement with the measurements. It is found that discrepancies with the experiments could be removed if the PESs were slightly more attractive. In this regard, the most attractive RCCSD(T)-CASPT2 PESs perform slightly better than the RCCSD(T)-MRCI counterpart.

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Diatom–diatom interactions: Building potential energy surfaces and effect of intramolecular vibrations

Cited by 5 publications

References 33 publications

First-principles description of van der Waals bonded spin-polarized systems using the vdW-DF+ U method: Application to solid oxygen at low pressure

First-principles description of van der Waals bonded spin-polarized systems using the vdW-DF+ U method: Application to solid oxygen at low pressure

An unrestricted approach for the accurate calculation of the interaction potentials of open-shell monomers: The case of O2–O2

Global ab initio potential energy surfaces for the O2(Σ3g−)+O2(Σ3g−) interaction

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