Common workflows for computing material properties using different quantum engines

The prediction of material properties based on density-functional theory has become routinely common, thanks, in part, to the steady increase in the number and robustness of available simulation packages. This plurality of codes and methods is both a boon and a burden. While providing great opportunities for cross-verification, these packages adopt different methods, algorithms, and paradigms, making it challenging to choose, master, and efficiently use them. We demonstrate how developing common interfaces for workflows that automatically compute material properties greatly simplifies interoperability and cross-verification. We introduce design rules for reusable, code-agnostic, workflow interfaces to compute well-defined material properties, which we implement for eleven quantum engines and use to compute various material properties. Each implementation encodes carefully selected simulation parameters and workflow logic, making the implementer’s expertise of the quantum engine directly available to non-experts. All workflows are made available as open-source and full reproducibility of the workflows is guaranteed through the use of the AiiDA infrastructure.This work is supported by the MARVEL National Centre of Competence in Research (NCCR) funded by the Swiss National Science Foundation (grant agreement ID 51NF40-182892) and by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 824143 (European MaX Centre of Excellence “Materials design at the Exascale”) and Grant Agreement No. 814487 (INTERSECT project). We thank M. Giantomassi and J.-M. Beuken for their contributions in adding support for PseudoDojo tables to the aiida-pseudo (https://github.com/aiidateam/aiida-pseudo) plugin. We also thank X. Gonze, M. Giantomassi, M. Probert, C. Pickard, P. Hasnip, J. Hutter, M. Iannuzzi, D. Wortmann, S. Blügel, J. Hess, F. Neese, and P. Delugas for providing useful feedback on the various quantum engine implementations. S.P. acknowledges support from the European Unions Horizon 2020 Research and Innovation Programme, under the Marie Skłodowska-Curie Grant Agreement SELPH2D No. 839217 and computer time provided by the PRACE-21 resources MareNostrum at BSC-CNS. E.F.-L. acknowledges the support of the Norwegian Research Council (project number 262339) and computational resources provided by Sigma2. P.Z.-P. thanks to the Faraday Institution CATMAT project (EP/S003053/1, FIRG016) for financial support. KE acknowledges the Swiss National Science Foundation (grant number 200020-182015). G.Pi. and K.E. acknowledge the swissuniversities “Materials Cloud” (project number 201-003). Work at ICMAB is supported by the Severo Ochoa Centers of Excellence Program (MICINN CEX2019-000917-S), by PGC2018-096955-B-C44 (MCIU/AEI/FEDER, UE), and by GenCat 2017SGR1506. B.Z. thanks to the Faraday Institution FutureCat project (EP/S003053/1, FIRG017) for financial support. J.B. and V.T. acknowledge support by the Joint Lab Virtual Materials Design (JLVMD) of the Forschungszentrum Jülich.Peer reviewe

Computational Exploration of IRMOFs for Xenon Separation from Air

Metal–organic frameworks (MOFs) found their well-deserved position in the field of gas adsorption and separation because of their unique properties. The separation of xenon from different gas mixtures containing this valuable and essential noble gas is also benefited from the exciting nature of MOFs. In this research, we chose a series of isoreticular MOFs as our study models to apply advanced molecular simulation techniques in the context of xenon separation from air. We investigated the separation performance of our model set through simulation of ternary gas adsorption isotherms and consequent calculation of separation performance descriptors, finding out that IRMOF-7 shows better recovering capabilities compared to the other studied MOFs. We benefited from visualization of xenon energy landscape within MOFs to obtain valuable information on possible reasoning behind our observations. We also examined temperature-based separation performance boosting strategy. Additionally, we noted that although promising candidates are present among the studied MOFs for xenon recovery from air, they are not suitable for xenon recovery from exhaled anesthetic gas mixture

Theoretical Assessment of the Selective Fluorescence Quenching of 1‑Amino-8-naphthol-3,6-disulfonic Acid (H-Acid) Complexes with Zn²⁺, Cd²⁺, and Hg²⁺: A DFT and TD-DFT Study

Density functional theory (DFT) and time-dependent (TD)-DFT calculations at the PBE0/6-31++G** aug-cc-PVDZ (along with corresponding ECP for metal ions) level of theory were carried out to investigate the differences in structure, bonding, and fluorescence behavior of 1-amino-8-naphthol-3,6-disulfonic acid (H-acid) (<b>1</b>) when coordinated to Zn²⁺ (<b>2</b>), Cd²⁺ (<b>3</b>), and Hg²⁺ (<b>4</b>) in a simulated continuous aqueous media (PCM). Ground and excited state calculations were performed on all compounds in order to gain insight on their bonding properties, as well as on their photochemical behavior, since we previously reported that complexation of Hg²⁺ quenches the fluorescence properties of ligand (<b>1</b>), while at the same time exhibits a different coordination pattern than the two other remaining complexes. Changes in the excited states’ radiative lifetime upon coordination to different metals account for this selective quenching

Phase segregation and nanoconfined fluid O2 in a lithium-rich oxide cathode

Lithium-rich oxide cathodes lose energy density during cycling due to atomic disordering and nanoscale structural rearrangements, both of which are challenging to characterise. Here, we resolve the kinetics and thermodynamics of these processes in an exemplar layered Li-rich cathode, Li1.2–xMn0.8O2 by using a combined approach of ab initio molecular dynamics and cluster-expansion-based Monte Carlo simulations. We identify a kinetically accessible and thermodynamically favoured mechanism to form O2 molecules in the bulk, involving Mn migration and driven by interlayer oxygen dimerisation. At the top of charge the bulk structure locally phase-segregates into MnO2-rich regions and Mn-deficient nanovoids, which contain O2 molecules as a nanoconfined fluid. These nanovoids are connected in a percolating network, potentially allowing long-range oxygen transport, and linking bulk O2 formation to surface O2 loss. These insights highlight the importance of future strategies to kinetically stabilise the bulk structure of Li-rich O-redox cathodes to maintain their high energy densities

Selective Optical Sensing of Hg(II) in Aqueous Media by H‑Acid/SBA-15: A Combined Experimental and Theoretical Study

The H-acid dye intermediate was successfully attached to the SBA-15 mesoporous silica surface in a two-step modification process. Synthesized materials were characterized using several techniques including Fourier transform infrared spectroscopy, N2 adsorption–desorption measurements, small-angle X-ray scattering, transmission electron microscopy, and thermogravimetric analysis. The fluorescent sensing properties were examined in the final product toward several metal ions and showed high selectivity for Hg²⁺. Computational studies were performed in order to obtain a detailed electronic description of the quenching mechanism of H-acid fluorescence by Hg²⁺ as well as studying the structure and bonding in the [H-acid]­Hg²⁺ complex

Heads or Tails? Sandwich-Type Metallocomplexes of Hexakis(2,3-di-O-methyl)-α-cyclodextrin

Native and synthetically modified cyclodextrins (CDs) are useful building blocks in construction of large coordination complexes and porous materials with various applications. Sandwich-type complexes (STCs) are one of the important groups in this area. Usually, coordination of secondary hydroxyls or the “head” portal of native CD molecules to a notional multinuclear ring of metal cations leads to formation of head-to-head STCs. Our study introduces a new CD-ligand, hexakis(2,3-di-O-methyl)-α-cyclodextrin, which enables formation of intriguing head-to-head, but also novel tail-to-tail STCs. Homometallic silver-based head-to-head STCs, AgPF6-STC and AgClO4-STC, were obtained by coordination of ligand methoxy groups to six Ag+, while bulky counter-anions are located on the outside but also filling the inner space of infinite linear channels formed. In contrast, unique homometallic tail-to-tail RbF-STC was prepared by complexation of primary hydroxyls, “tails”, to twelve Rb+ tightly interconnected by twelve F- creating complex structure with accessible pores for potential gas adsorptions.peerReviewe

Accessing polyanionic redox in high voltage Li-rich thiophosphates

In the search for novel positive electrode materials for lithium-ion cells, Li-rich sulfides are attracting increasing interest. Despite the success of polyoxyanion-based cathodes such as LiFePO4, their thiophosphate counterparts have remained largely unexplored. Here, the Li-rich thiophosphate Li2FeP2S6, which exhibits the highest known voltage (3 V) for a sulfide electrode, is investigated in a solid-state configuration. Through examination of isostructural transition-metal substitutions, we identify a novel Mn-substituted compound, Li2Fe0.8Mn0.2P2S6, with higher capacity than the parent Fe system while maintaining the high voltage. Hard X-ray Photoelectron Spectroscopy and ab initio molecular dynamics simulations indicate that Mn substitution activates P2S6 polyanionic redox involving interlayer S--S bond formation with no evidence of Fe or Mn cation migration, and increases capacity beyond the formal transition-metal redox limit. This demonstration of polyanionic redox in a thiophosphate material highlights the opportunity to explore alternative Li-rich thiophosphate structures as high-capacity lithium-ion cathodes