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In this study, the effect of nitrogen substitution in wolframite-type ScTaO4 was investigated using density- functional theory calculations. First, structural and mechanical properties, as well as the dynamical stability of ScTaO4 were examined deeply for the ambient-pressure structure. Subsequently, we studied how lattice vibrations are affected by hydrostatic pressure and determined the elastic moduli of ScTaO4. The results of our study show that the monoclinic structure of ScTaO4 is rigid and non-compressible. In addition, band- structure calculations show that ScTaO4 has a wide direct band-gap of 4.04 eV, which in turn leads to a possible tuning of electronic properties. We have found that this task can be conducted by partially substi- tuting oxygen atoms in the unit cell with nitrogen atoms. Both band-structure calculations and charge- density analyses revealed a narrowing in the band gap caused by the presence of nitrogen atoms, which act as a shallow acceptor state, resulting in weak repulsive interactions and structural distortions in both Sc and Ta coordination polyhedra; reducing the crystal symmetry from monoclinic to triclinic.

The ability to control the chemical conformation of a system via external stimuli is a promising route for developing molecular switches. For eventual deployment as viable sub-nanoscale components that are compatible with current electronic device technology, conformational switching should be controllable by a local electric field (i.e. E-field gateable) and accompanied by a rapid and significant change in conductivity. In organic chemical systems the degree of π-conjugation is linked to the degree of electronic delocalisation, and thus largely determines the conductivity. Here, by means of accurate first principles calculations, we study the prototypical biphenyl based molecular system in which the dihedral angle between the two rings determines the degree of conjugation. In order to make this an E-field gateable system we create a net dipole by asymmetrically functionalising one ring with: (i) electron withdrawing (F, Br and CN), (ii) electron donating (NH2), and (iii) mixed (NH2/NO2) substituents. In this way, the application of an E-field interacts with the dipolar system to influence the dihedral angle, thus controlling the conjugation. For all considered substituents we consider a range of E-fields, and in each case extract conformational energy profiles. Using this data we obtain the minimum E-field required to induce a barrierless switching event for each system. We further extract the estimated switching speeds, the conformational probabilities at finite temperatures, and the effect of applied E-field on electronic structure. Consideration of these data allow us to assess which factors are most important in the design of efficient gateable electrical molecular switches.

The new class of oxide heterojunctions with mixed dimensionalities holds great promise for energy and environmental applications. However, the existing fabrication strategies typically involve low-yield and multistep processes leading to the formation of powders that necessitate binding agents when used for electrochemical applications; thereby, the durability and performance of the resultant electrode may be adversely impacted. To address these challenges, the present work first reports a high-temperature counter-current gas flow technique for rapid fabrication (5–10 min) of centimetre-size, self-adhesive, free-standing 3D patches made of ZnO-based woven nanowires. Furthermore, the high applicability of the method was shown by layer-by-layer assembly of the ZnO and layers of 0D heteroatoms including Bi2O3, CdO, SnO2, and carbon forming stratified oxide heterojunction (SOH) nanostructures with midgap states within their electronic bandgap region. This work is innovative in that the ZnO and the fabricated SOHs are synthesised through a sustainable and large-scale method based on microrecycling of waste materials. The engineering of the electronic band positions can modify the functionality of the SOH patches by optimising the potentials required for catalytic reactions. As a representative, the SOH nanostructures were tested for anodic electrocatalytic water oxidation to H2O2. The results showed that the ZnO–CdO patch has the lowest overpotential of 150 mV and outstanding stability at 2.33 V vs. RHE. Furthermore, the results of first-principles density functional theory (DFT) calculations (i) confirmed realignments of the band position due to the formation of midgap states, and (ii) revealed that significant improvements in the electrocatalytic H2O2 performance can be achieved with overpotentials as low as 0.19 and 0.31 V for ZnO–CdO and ZnO–Bi2O3, respectively. This work offers an ultrafast fabrication strategy to synthesise binder-free SOH nanostructures with an engineered electronic structure that can be an alternative to state-of-the-art noble metal electrocatalysts such as Pt.

Over recent decades, much effort has been made to lengthen spin relaxation/decoherence times of single-molecule magnets and molecular qubits by following different chemical design rules such as maximizing the total spin value, controlling symmetry, enhancing the ligand field or inhibiting key vibrational modes. Simultaneously, electronic structure calculations have been employed to provide an understanding of the processes involved in the spin dynamics of molecular systems and served to refine or introduce new design rules. This review focuses on contemporary theoretical approaches focused on the calculation of spin relaxation/decoherence times, highlighting their main features and scope. Fundamental aspects of experimental techniques for the determination of key Single Molecule Magnet/Spin Qubit properties are also reviewed.

Nonlinear optical properties (NLOPs) play a major role in photonics, electro-optics and optoelectronics, and other fields of modern optics. The design of new NLO molecules and materials has benefited from the development of computational tools to analyze the relationship between the electronic structure of molecules and their optical response. In this paper, we present a new means to analyze the response property through the partition of NLOPs in terms of orbital contributions (PNOC). This tool can be used to obtain a real-space representation of the NLOPs, providing a powerful visualization aid to connect the magnitude of the optical property with some parts of the molecule. Unlike other methods to analyze NLOPs, the PNOC decomposes the optical property into orbitals of the unperturbed system, furnishing this method with the ability to assess the performance of single- and multi-determinant electronic structure methods. PNOC can be also used to design small basis sets for an accurate description of large systems, saving a substantial amount of computer time for the calculation of optical properties This research has been funded by Spanish MINECO/FEDER Projects CTQ2014-52525-P and EUIN2017-88605, the Catalan DIUE 2014SGR931 and IKERBASQUE

Anions have often been considered to act essentially as electron donors or acceptors in molecular conductors. However there is now growing evidence that they play an essential role in directing the structural and hence electronic properties of many of these systems. After reviewing the basic interactions and different ground states occurring in molecular conductors we consider in detail how anions influence the structure of donor stacks and often guide them toward different types of transitions. Consideration of the Bechgaard and Fabre salts illustrates how anions play a crucial role in directing these salts through complex phase diagrams where different conducting and localized states are in competition. We also emphasize the important role of hydrogen bonding and conformational flexibility of donors related to BEDT-TTF and we discuss how anions have frequently a strong control of the electronic landscape of these materials. Charge ordering, metal to metal and metal to insulator transitions occurring in these salts are considered., Work in Spain was supported by MINECO (Spain) through Grants FIS2015-64886-C5-4-P and CTQ2015-64579-C3-3-P, and Generalitat de Catalunya (2017SGR1506, 2017SGR1289 and XRQTC). E. C. acknowledges support of the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2015-0496. This review is based on recent collaborative works and pertinent discussions with N. Avarvari, P. Batail, C. Bourbonnais, C. Coulon, M. de Souza, M. Dressel, M. Fourmigue´, P. Foury-Leylekian, V. Ilakovac, D. Je´rome, M. Lang, E. Molins, Y. Nogami, C. Pasquier, H. Sawa and S. Tomic´.

Despite B and Al belong to the same group 13 elements, the B6²- cluster prefers the planar D2h geometry, whereas Al6²- favours the Oh structure. In this work, we analyse the origin of the relative stability of the D2h and Oh forms in these clusters by means of an energy decomposition analysis based on the turn-upside-down approach. Our results show that what causes the different trend observed is the orbital interaction term, which combined with the electrostatic component do (Al6²- and Ga6²-) or do not (B6²-) compensate the higher Pauli repulsion of the Oh form. Analysing the orbital interaction term in more detail, we find that the preference of B6²- for the planar D2h form has to be attributed to two particular molecular orbital interactions. Our results are in line with a dominant delocalisation force in Al clusters and the preference for more localised bonding in B metal clusters. For mixed clusters, we have found that those with more than two B atoms prefer the planar structure for the same reasons as for B6²- This work has been supported by the Ministerio de Economía y Competitividad (MINECO) of Spain (Project CTQ2014-54306-P) and the Generalitat de Catalunya (project 2014SGR931, Xarxa de Referència en Química Teòrica i Computacional, ICREA Academia 2014 prize for M.S., and grant No. 2014FI_B 00429 to O.E.B.). The EU under the FEDER grant UNGI10-4E-801 (European Fund for Regional Development)has also funded this research. J. P. thanks the National Research School Combination - Catalysis (NRSCC), and The Netherlands Organization for Scientific Research (NWO/CW and NWO/NCF)

Triarylmethyls (TAMs) are a class of long-lived purely organic radicals discovered at the beginning of the twentieth century. The chemical versatility and high stability of TAMs have lead to their application in many fields of science and technology. All compounds of this class are composed of three aryl rings bonded to a central carbon atom, where their unpaired electron mainly resides. Due to the π-conjugated electronic nature of this molecular structure, the possibility arises of controlling the unpaired electron localization (i.e. spin localization) by the torsion angles of the three aryl rings. By using density functional theory calculations (DFT) we have carefully investigated this phenomenon for a wide range of TAMs and probed how it is influenced by other important parameters such as chemical functionalization and temperature. Our results demonstrate that a single general spin versus structure relation is followed for all of our studied TAMs confirming that having a predictable structure-dependent spin localisation is an intrinsic feature of these radicals. Considering that spin localisation in TAMs is linked to many other important properties (e.g. magnetic interactions, optical absorption bands, magnetoresistance phenomena), the fact that manipulation of aryl ring twist angles could lead to molecular level control over such features presents enormous potential for future scientific and technological applications.

New insights into the double bond isomerization of fulvene in the ground and excited electronic states are provided by newly developed QTAIM and stress tensor tools. The S0 and S1 states follow the 'biradical' torsion model, but the double bond is stiffer in the S0 state; by contrast, the S2 state follows the 'zwitterionic' torsion. Differences are explained in terms of the ellipticity and bond critical point (BCP) stiffness for both QTAIM and the stress tensor. Overall, the wave-function based analysis is found to be in agreement with the work of Bonačić-Koutecký and Michl that the bond-twisted species can have biradical or zwitterionic character, depending on the state. Using QTAIM and the stress tensor a new understanding of bond torsion is revealed; the electronic charge density around the twisted bond is found not to rotate in concert with the nuclei of the rotated -CH2 methylene group. The ability to visualize how the bond stiffness varies between individual electronic states and how this correlates with the QTAIM and stress tensor bond stiffness is highlighted. In addition, the most and least preferred morphologies of bond-path torsion are visualized. Briefly we discuss the prospects for using this new QTAIM and stress tensor analysis for excited state chemistry The One Hundred Talents Foundation of Hunan Province and the aid program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province are gratefully acknowledged for the support of S.J. and S. R. K. The National Natural Science Foundation of China is also gratefully acknowledged for the support of S.J. and S. R. K, project approval number: 21273069. L. B. acknowledges support from the Spanish Ministerio de Economia y Sostenibilidad (MINECO) (CTQ2011-26573 and UNGI08-4E-003 from FEDER (European Fund for Regional Development)), and the Catalan Agencia de Gestio d'Ajuts Universitaris i de Recerca (SGR0528) and Direccio General de la Recerca (Xarxa de Referencia en Quimica Teorica i Computacional de Catalunya)