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Publications 20232024-03-27T14:06:43+01:00

Publications (2023)

Total peer-reviewed articles: 111

Confining CO2 inside sI clathrate-hydrates: The impact of the CO2-water interaction on quantized dynamics

Authors: Valdes, Alvaro; Cabrera-Ramirez, Adriana; Prosmiti, Rita

Journal: JOURNAL OF COMPUTATIONAL CHEMISTRY

Publication date: 2023/06/30

DOI: 10.1002/jcc.27110

Abstract: We report new results on the translational-rotational (T-R) states of the CO2 molecule inside the sI clathrate-hydrate cages. We adopted the multiconfiguration time-dependent Hartree methodology to solve the nuclear molecular Hamiltonian, and to address issues on the T-R couplings. Motivated by experimental X-ray observations on the CO2 orientation in the D and T sI cages, we aim to evaluate the effect of the CO2-water interaction on quantum dynamics. Thus, we first compared semiempirical and ab initio-based pair interaction model potentials against first-principles DFT-D calculations for ascertaining the importance of nonadditive many-body effects on such guest-host interactions. Our results reveal that the rotational and translational excited states quantum dynamics is remarkably different, with the pattern and density of states clearly affected by the underlying potential model. By analyzing the corresponding the probability density distributions of the calculated T-R eigenstates on both semiempirical and ab initio pair CO2-water nanocage potentials, we have extracted information on the altered CO2 guest local structure, and we discussed it in connection with experimental data on the orientation of the CO2 molecule in the D and T sI clathrate cages available from neutron diffraction and C-13 solid-state NMR studies, as well as in comparison with previous molecular dynamics simulations. Our calculations provide a very sensitive test of the potential quality by predicting the low-lying T-R states and corresponding transitions for the encapsulated CO2 molecule. As such spectroscopic observables have not been measured so far, our results could trigger further detailed experimental and theoretical investigations leading to a quantitative description of the present guest-host interactions.

Computational investigations of stable multiple-cage-occupancy He clathrate-like hydrostructures

Authors: Yanes-Rodriguez, Raquel; Prosmiti, Rita

Journal: PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Publication date: 2023/06/28

DOI: 10.1039/d3cp00603d

Abstract: One of the several possibilities offered by the interesting clathrate hydrates is the opportunity to encapsulate several atoms or molecules, in such a way that more efficient storage materials could be explored or new molecules that otherwise do not exist could be created. These types of applications are receiving growing attention from technologists and chemists, given the future positive implications that they entail. In this context, we investigated the multiple cage occupancy of helium clathrate hydrates, to establish stable novel hydrate structures or ones similar to those predicted previously by experimental and theoretical studies. To this purpose, we analyzed the feasibility of including an increased number of He atoms inside the small (D) and large (H) cages of the sII structure through first-principles properly assessed density functional approaches. On the one hand, we have computed energetic and structural properties, in which we examined the guest-host and guest-guest interactions in both individual and two-adjacent clathrate-like sII cages by means of binding and evaporation energies. On the other hand, we have carried out a thermodynamical analysis on the stability of such He-containing hydrostructures in terms of changes in enthalpy, Delta H, Gibbs free energy, Delta G, and entropy, Delta S, during their formation process at various temperature and pressure values. In this way, we have been able to make a comparison with experiments, reaffirming the ability of computational DFT approaches to describe such weak guest-host interactions. In principle, the most stable structure involves the encapsulation of one and four He atoms inside the D and H sII cages, respectively; however, more He atoms could be entrapped under lower temperature and/or higher pressure thermodynamic conditions. We foresee such accurate computational quantum chemistry approaches contributing to the current emerging machine-learning model development.

Superfluid helium droplet-mediated surface-deposition of neutral and charged silver atomic species

Authors: Fernandez, Berta; Pi, Marti; de Lara-Castells, Maria Pilar

Journal: PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Publication date: 2023/06/28

DOI: 10.1039/d3cp01303k

Abstract: Experimental and theoretical work has delivered evidence of the helium nanodroplet-mediated synthesis and soft-landing of metal nanoparticles, nanowires, clusters, and single atoms on solid supports. Recent experimental advances have allowed the formation of charged metal clusters into multiply charged helium nanodroplets. The impact of the charge of immersed metal species in helium nanodroplet-mediated surface deposition is proved by considering silver atoms and cations at zero-temperature graphene as the support. By combining high-level ab initio intermolecular interaction theory with a full quantum description of the superfluid helium nanodroplet motion, evidence is presented that the fundamental mechanism of soft-deposition is preserved in spite of the much stronger interaction of charged species with surfaces, with high-density fluctuations in the helium droplet playing an essential role in braking them. Corroboration is also presented that the soft-landing becomes favored as the helium nanodroplet size increases.

Kibble-Zurek mechanism of Ising domains

Authors: Du, Kai; Fang, Xiaochen; Won, Choongjae; De, Chandan; Huang, Fei-Ting; Xu, Wenqian; You, Hoydoo; Gomez-Ruiz, Fernando J.; del Campo, Adolfo; Cheong, Sang-Wook

Journal: NATURE PHYSICS

Publication date: 2023/06/26

DOI: 10.1038/s41567-023-02112-5

Abstract: The formation of topological defects after a symmetry-breaking phase transition is an overarching phenomenon that encodes the underlying dynamics. The Kibble-Zurek mechanism (KZM) describes these non-equilibrium dynamics of second-order phase transitions and predicts a power-law relationship between the cooling rates and the density of topological defects. It has been verified as a successful model in a wide variety of physical systems, including structure formation in the early Universe and condensed-matter materials. However, it is uncertain if the KZM mechanism is also valid for topologically trivial Ising domains, one of the most common and fundamental types of domain in condensed-matter systems. Here we show that the cooling rate dependence of Ising domain density follows the KZM power law in two different three-dimensional structural Ising domains: ferro-rotation domains in NiTiO3 and polar domains in BiTeI. However, although the KZM slope of NiTiO3 agrees with the prediction of the 3D Ising model, the KZM slope of BiTeI exceeds the theoretical limit, providing an example of steepening KZM slope with long-range dipolar interactions. Our results demonstrate the validity of KZM for Ising domains and reveal an enhancement of the power-law exponent for transitions of non-topological quantities with long-range interactions. The Kibble-Zurek mechanism is shown to apply to structural Ising domains in three-dimensional materials. Long-range interactions modify the critical exponents away from theoretical predictions.

Infrared spectra of solid indene pure and in water ice: implications for observed IR absorptions in TMC-1

Authors: Mate, Belen; Tanarro, Isabel; Timon, Vicente; Cernicharo, Jose; Herrero, Victor J.

Journal: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Publication date: 2023/06/22

DOI: 10.1093/mnras/stad1761

Abstract: Experimental and theoretical infrared spectra, between 4000 and 500 cm(-1) (2.5-20 & mu;m), and infrared band strengths of two solid phases of indene, amorphous, and crystalline, are given for the first time. The samples were generated via vapour deposition under high vacuum conditions on a cold surface. Density functional theory was employed for the calculations of the infrared (IR) spectra. For lack of previous information, a monoclinic symmetry is suggested for the theoretical crystalline phase of indene, based on the comparison of the calculated and experimental IR spectra. Assignments, based on the calculations, are given for the main indene IR absorptions. The infrared spectra of highly diluted mixtures of indene in amorphous solid water at 10 K are also provided, evidencing that the indene spectrum is not much altered by the water ice environment. These data are expected to be useful for the search of this species in the solid phase in astrophysical environments with the JWST. With the band strengths obtained in this work, and applying a simple literature model, we find that indene could represent at most 2-5 per cent of the intensity of a weak absorption feature at 3.3 & mu;m recently reported for Elias 16. A column density of (1.5-0.6) x 10(16) cm(-2) is estimated for indene in the ice mantles of TMC-1. It would correspond to & AP; (2-0.8) x 10(-2) of cosmic carbon, which is probably too high for a single small hydrocarbon.

Photodissociation dynamics of methylamine in the blue edge of the A-band. I. The H-atom elimination channel

Authors: Recio, Pedro; Cachon, Javier; Zanchet, Alexandre; Poullain, Sonia Marggi; Banares, Luis

Journal: JOURNAL OF CHEMICAL PHYSICS

Publication date: 2023/06/21

DOI: 10.1063/5.0152993

Abstract: The photodissociation dynamics of methylamine (CH3NH2) upon excitation in the blue edge of the first absorption A-band, in the 198-203 nm range, are investigated by means of nanosecond pump-probe laser pulses and velocity map imaging combined with H(S-2)-atom detection through resonance enhanced multiphoton ionization. The images and corresponding translational energy distributions for the H-atoms produced show three different contributions associated with three reaction pathways. The experimental results are complemented by high-level ab initio calculations. The potential energy curves computed as a function of the N-H and C-H bond distances allow us to draw a picture of the different mechanisms. Major dissociation occurs through N-H bond cleavage and it is triggered by an initial geometrical change, i.e., from a pyramidal configuration of the C-NH2 with respect to the N atom to a planar geometry. The molecule is then driven into a conical intersection (CI) seam where three outcomes can take place: first, threshold dissociation into the second dissociation limit, associated with the formation of CH3NH((A) over tilde), is observed; second, direct dissociation after passage through the CI leading to the formation of ground state products; and third, internal conversion into the ground state well in advance to dissociation. While the two last pathways were previously reported at a variety of wavelengths in the 203-240 nm range, the former had not been observed before to the best of our knowledge. The role of the CI and the presence of an exit barrier in the excited state, which modify the dynamics leading the two last mechanisms, are discussed considering the different excitation energies used.

Blueprint for a Molecular-Spin Quantum Processor

Authors: Chiesa, A.; Roca, S.; Chicco, S.; de Ory, M. C.; Gomez-Leon, A.; Gomez, A.; Zueco, D.; Luis, F.; Carretta, S.

Journal: PHYSICAL REVIEW APPLIED

Publication date: 2023/06/21

DOI: 10.1103/PhysRevApplied.19.064060

Abstract: The implementation of a universal quantum processor still poses fundamental issues related to error mitigation and correction, which demand investigation of also platforms and computing schemes alternative to the main stream. A possibility is offered by employing multilevel logical units (qudits), naturally provided by molecular spins. Here we present the blueprint of a molecular spin quantum processor consisting of single molecular nanomagnets, acting as qudits, placed within superconducting resonators adapted to the size and interactions of these molecules to achieve a strong single spin-to-photon coupling. We show how to implement a universal set of gates in such a platform and to readout the final qudit state. Singlequdit unitaries (potentially embedding multiple qubits) are implemented by fast classical drives, while an alternative scheme is introduced to obtain two-qubit gates via resonant photon exchange. The latter is compared to the dispersive approach, finding in general a significant improvement. The performance of the platform is assessed by realistic numerical simulations of gate sequences, such as Deutsch-Josza and quantum simulation algorithms. The very good results demonstrate the feasibility of the molecular route towards a universal quantum processor.

First detection of the HSO radical in space?

Authors: Marcelino, N.; Puzzarini, C.; Agundez, M.; Fuentetaja, R.; Tercero, B.; de Vicente, P.; Cernicharo, J.

Journal: ASTRONOMY & ASTROPHYSICS

Publication date: 2023/06/20

DOI: 10.1051/0004-6361/202346935

Abstract: We report the discovery of HSO towards several cold dark clouds. The detection is confirmed by the observation of the fine and hyperfine components of two rotational transitions in the protostellar core B1-b, using the Yebes 40 m and IRAM 30 m telescopes. Furthermore, all the fine and hyperfine components of its fundamental transition 1(0,?1) – 0(0,?0) at 39 GHz were also detected toward the cyanopolyyne peak of TMC-1. The measured frequencies were used to improve the molecular constants and predict more accurate line frequencies. We also detected the strongest hyperfine component of the 1(0,?1) – 0(0,?0) transition of HSO toward the cold dark clouds L183, L483, L1495B, L1527, and Lupus-1A. The HSO column densities were obtained using LTE models that reproduce the observed spectra. The rotational temperature was constrained to 4.5 K in B1-b and TMC-1 using the available Yebes 40 m and IRAM 30 m data. The obtained column densities range between 7.0×10(10) cm(-2) and 2.9×10(11) cm(-2), resulting in abundances in the range of (1.4-7.0) x 10(-12) relative to H-2. Our observations show that HSO is widespread in cold dense cores. However, more observations, together with a detailed comparison with other S-bearing species, are needed to constrain the chemical production mechanisms of HSO, which are not considered in current models.

Carbon vacancy-assisted stabilization of individual Cu5 clusters on graphene. Insights from ab initio molecular dynamics

Authors: Carroll, Lenard L.; Moskaleva, Lyudmila V.; de Lara-Castells, Maria Pilar

Journal: PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Publication date: 2023/06/15

DOI: 10.1039/d2cp05843j

Abstract: Recent advances in synthesis and characterization methods have enabled the controllable fabrication of atomically precise metal clusters (AMCs) of subnanometer size that possess unique physical and chemical properties, yet to be explored. Such AMCs have potential applications in a wide range of fields, from luminescence and sensing to photocatalysis and bioimaging, making them highly desirable for further research. Therefore, there is a need to develop innovative methods to stabilize AMCs upon surface deposition, as their special properties are lost due to sintering into larger nanoparticles. To this end, dispersion-corrected density functional theory (DFT-D3) and ab initio molecular dynamics (AIMD) simulations have been employed. Benchmarking against high-level post-Hartree-Fock approaches revealed that the DFT-D3 scheme describes very well the lowest-energy states of clusters of five and ten atoms, Cu-5 and Cu-10. AIMD simulations performed at 400 K illustrate how intrinsic defects of graphene sheets, carbon vacancies, are capable of confining individual Cu-5 clusters, thus allowing for their stabilization. Furthermore, AIMD simulations provide evidence on the dimerization of Cu-5 clusters on defect-free graphene, in agreement with the ab initio predictions of (Cu-5)(n) aggregation in the gas phase. The findings of this study demonstrate the potential of using graphene-based substrates as an effective platform for the stabilization of monodisperse atomically precise Cu-5 clusters.

Isotope Effect in D2O Negative Ion Formation in Electron Transfer Experiments: DO-D Bond Dissociation Energy

Authors: Kumar, Sarvesh; Hoshino, Masamitsu; Kerkeni, Boutheina; Garcia, Gustavo; Limao-Vieira, Paulo

Journal: JOURNAL OF PHYSICAL CHEMISTRY LETTERS

Publication date: 2023/06/05

DOI: 10.1021/acs.jpclett.3c00786

Abstract: H2O/D2O negative ion time-of-flightmassspectra from electron transfer processes at different collision energieswith neutral potassium yield OH-/OD-, O-, and H-/D-. The branching ratios show a relevant energy dependence with animportant isotope effect in D2O. Electronic state spectroscopyof water has been further investigated by recording potassium cationenergy loss spectra in the forward scattering direction at an impactenergy of 205 eV (lab frame), with quantum chemical calculations forthe lowest-lying unoccupied molecular orbitals in the presence ofa potassium atom supporting most of the experimental findings. TheDO-D bond dissociation energy has been determined for the firsttime to be 5.41 +/- 0.10 eV. The collision dynamics revealed thecharacter of the singly excited (1b(2) (-1)) molecular orbital and doubly excited states in such K-H2O and K-D2O collisions.

The spatial distribution of an aromatic molecule, C6H5CN, in the cold dark cloud TMC-1

Authors: Cernicharo, J.; Tercero, B.; Marcelino, N.; Agundez, M.; de Vicente, P.

Journal: ASTRONOMY & ASTROPHYSICS

Publication date: 2023/06/05

DOI: 10.1051/0004-6361/202346722

Abstract: We present a highly sensitive 2D line survey of TMC-1 obtained with the Yebes 40 m radio telescope in the Q-band (31.13-49.53 GHz). These maps cover a region of 320 ” x320 ” centred on the position of the QUIJOTE line survey with a spatial sampling of 20 ”. The region covering 240 ” x240 ”, where a longer integration time was used, shows a homogenous sensitivity of 2-4 mK across the band. We present in this work the first determination of the spatial extent of benzonitrile (C6H5CN), which follows that of cyanopolyynes rather well, but differs significantly from that of the radicals CnH and CnN. We definitively conclude that aromatic species in TMC-1 are formed from chemical reactions involving smaller species in the densest zones of the cloud.

Quantum neural networks with multi-qubit potentials

Authors: Ban, Yue; Torrontegui, E.; Casanova, J.

Journal: SCIENTIFIC REPORTS

Publication date: 2023/06/05

DOI: 10.1038/s41598-023-35867-1

Abstract: We propose quantum neural networks that include multi-qubit interactions in the neural potential leading to a reduction of the network depth without losing approximative power. We show that the presence of multi-qubit potentials in the quantum perceptrons enables more efficient information processing tasks such as XOR gate implementation and prime numbers search, while it also provides a depth reduction to construct distinct entangling quantum gates like CNOT, Toffoli, and Fredkin. This simplification in the network architecture paves the way to address the connectivity challenge to scale up a quantum neural network while facilitating its training.

Probing and harnessing photonic Fermi arc surface states using light-matter interactions

Authors: Garcia-Elcano, Inaki; Merino, Jaime; Bravo-Abad, Jorge; Gonzalez-Tudela, Alejandro

Journal: SCIENCE ADVANCES

Publication date: 2023/06/02

DOI: 10.1126/sciadv.adf8257

Abstract: Fermi arcs, i.e., surface states connecting topologically distinct Weyl points, represent a paradigmatic manifes-tation of the topological aspects of Weyl physics. We investigate a light-matter interface based on the photonic counterpart of these states and prove that it can lead to phenomena with no analog in other setups. First, we show how to image the Fermi arcs by studying the spontaneous decay of one or many emitters coupled to the system’s border. Second, we demonstrate that, exploiting the negative refraction of these modes, the Fermi arc surface states can act as a robust quantum link, enabling, e.g., the occurrence of perfect quantum state transfer between the considered emitters or the formation of highly entangled states. In addition to their fundamental interest, our findings evidence the potential offered by the photonic Fermi arc light-matter interfaces for the design of more robust quantum technologies.

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