| 1. |
- Charry, Jorge, et al.
(författare)
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The three-center two-positron bond
- 2022
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 13:46, s. 13795-13802
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Tidskriftsartikel (refereegranskat)abstract
- Computational studies have shown that one or more positrons can stabilize two repelling atomic anions through the formation of two-center positronic bonds. In the present work, we study the energetic stability of a system containing two positrons and three hydride anions, namely 2e+[H33−]. To this aim, we performed a preliminary scan of the potential energy surface of the system with both electrons and positrons in a spin singlet state, with a multi-component MP2 method, that was further refined with variational and diffusion Monte Carlo calculations, and confirmed an equilibrium geometry with D3h symmetry. The local stability of 2e+[H33−] is demonstrated by analyzing the vertical detachment and adiabatic energy dissociation channels. Bonding properties of the positronic compound, such as the equilibrium interatomic distances, force constants, dissociation energies, and bonding densities are compared with those of the purely electronic H3+ and Li3+ systems. Through this analysis, we find compelling similarities between the 2e+[H33−] compound and the trilithium cation. Our results strongly point out the formation of a non-electronic three-center two-positron bond, analogous to the well-known three-center two-electron counterparts, which is fundamentally distinct from the two-center two-positron bond [D. Bressanini, J. Chem. Phys., 2021, 155, 054306], thus extending the concept of positron bonded molecules.
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| 2. |
- Holm, Alexander, 1983-, et al.
(författare)
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A Water-Promoted Mars-van Krevelen Reaction Dominates Low-Temperature CO Oxidation over Au-Fe2O3 but Not over Au-TiO2
- 2024
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Ingår i: ACS Catalysis. - 2155-5435. ; 14:5, s. 3191-3197
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Tidskriftsartikel (refereegranskat)abstract
- We provide experimental evidence that is inconsistent with often proposed Langmuir−Hinshelwood (LH) mechanistic hypotheses for water-promoted CO oxidation over Au–Fe2O3. Passing CO and H2O, but no O2, over Au-γ-Fe2O3 at 25 °C, we observe significant CO2 production, inconsistent with LH mechanistic hypotheses. Experiments with H218O further show that previous LH mechanistic proposals cannot account for water-promoted CO oxidation over Au-γ-Fe2O3. Guided by density functional theory, we instead postulate a water-promoted Mars–van Krevelen (w-MvK) reaction. Our proposed w-MvK mechanism is consistent both with observed CO2 production in the absence of O2 and with CO oxidation in the presence of H218O and 16O2. In contrast, for Au-TiO2, our data is consistent with previous LH mechanistic hypotheses.
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| 3. |
- Moncada, Félix, 1989-, et al.
(författare)
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A nuclear configuration interaction approach to study nuclear spin effects : an application to ortho- and para-3He2@C60
- 2024
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Ingår i: ChemPhysChem. - 1439-4235 .- 1439-7641. ; 25:4
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a non-orthogonal configuration interaction approach to investigate nuclear quantum effects on energies and densities of confined fermionic nuclei. The Hamiltonian employed draws parallels between confined systems and many-electron atoms, where effective non-Coulombic potentials represent the interactions of the trapped particles. One advantage of this method is its generality, as it offers the potential to study the nuclear quantum effects of various confined species affected by effective isotropic or anisotropic potentials. As a first application, we analyze the quantum states of two 3He atoms encapsulated in C60. At the Hartree–Fock level, we observe the breaking of spin and spatial symmetries. To ensure wavefunctions with the correct symmetries, we mix the broken-symmetry Hartree–Fock states within the non-orthogonal configuration interaction expansion. Our proposed approach predicts singly and triply degenerate ground states for the singlet (para-3He2@C60) and triplet (ortho-3He2@C60) nuclear spin configurations, respectively. The ortho-3He2@C60 ground state is 5.69 cm−1 higher in energy than the para-3He2@C60 ground state. The nuclear densities obtained for these states exhibit the icosahedral symmetry of the C60 embedding potential. Importantly, our calculated energies for the lowest 85 states are in close agreement with perturbation theory results based on a harmonic oscillator plus rigid rotor model of 3He2@C60.
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| 4. |
- Moncada, Felix, 1989-, et al.
(författare)
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Multicomponent wavefunction-in-DFT embedding for positronium molecules
- 2023
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 158:13
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Tidskriftsartikel (refereegranskat)abstract
- This work presents an extension of the projector operator embedding scheme of Manby et al. [J. Chem. Theory Comput. 8, 2564 (2012)] in a multicomponent (MC) framework. Here, a molecular system containing electrons and other types of quantum species is divided into a wavefunction (WF) subsystem of interest and a density functional theory (DFT) environment. The WF-in-DFT partition decreases computational costs by partially truncating the WF subsystem basis set at the cost of introducing a controllable embedding error. To explore the applicability of the MC extension, third-order propagator-in-DFT calculations were performed for positron–anion complexes for alkoxides and carboxylates with carbon chains of different sizes. For these systems, it was found that selecting a WF subsystem with the positron and only the oxygen atoms caused an error of 0.1 eV or lower in positron-binding energies, while reducing between 33% and 55% the basis set size. The reduction of computational costs achieved with the embedding scheme allowed us to improve molecular positron-binding energy predictions by performing complete basis set limit extrapolations. Combining the WF-in-DFT embedding and the complete basis set extrapolation, positronium aliphatic alkoxides were predicted to be energetically stable by 0.3 eV with respect to Ps emission. Similarly, positronium carboxylates, both aromatic and aliphatic, were predicted to be stable by 1.3 eV.
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| 5. |
- Omar, Karwan A., et al.
(författare)
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Current status of deMon2k for the investigation of the early stages of matter irradiation by time-dependent DFT approaches
- 2023
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Ingår i: The European Physical Journal Special Topics. - 1951-6355 .- 1951-6401. ; 232, s. 2167-2193
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Forskningsöversikt (refereegranskat)abstract
- We summarize in this article the recent progress made in our laboratories in the development of numerical approaches dedicated to investigating ultrafast physicochemical responses of biological matter subjected to ionizing radiations. Our modules are integrated into the deMon2k software which is a readily available program with highly optimized algorithms for conducting Auxiliary Density Functional Theory (ADFT) calculations. We have developed a computational framework based on Real-Time Time-dependent ADFT to simulate the electronic responses of molecular systems to strong perturbations, while molecular dynamics simulations in the ground and excited states (Ehrenfest dynamics) are available to simulate irradiation-induced ultrafast bond breaking/formation. Constrained ADFT and Multi-component ADFT have also been incorporated to simulate charge transfer processes and nuclear quantum effects, respectively. Finally, a coupling to polarizable force fields further permits to realistically account for the electrostatic effects that the systems' environment has on the perturbed electron density. The code runs on CPU or hybrid CPU/GPU architectures affording simulations of systems comprised up to 1000 atoms at the DFT level with controlled numerical accuracy. We illustrate the applications of these methodologies by taking results from our recent articles that aimed principally at understanding experimental data from pulse radiolysis experiments.
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