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We review the most significant results obtained in the study of isolated nucleobases in solution by quantum mechanical methods, trying to highlight also the most relevant open issues. We concisely discuss some methodological issues relevant to the study of molecular electronic excited molecular states in condensed phases, focussing on the methods most commonly applied to the study of nucleobases, i.e. continuum models as the Polarizable Continuum Model and explicit solvation models. We analyse how the solvent changes the relative energy of the lowest energy excited states in the Franck-Condon region, their minima and the Conical Intersections among the different states, interpreting the experimental optical spectra, both steady state and time-resolved. Several methods are available for accurately including solvent effects in the Franck-Condon region, and for most of the nucleobases the solvent shift on the different excited states can be considered assessed. The study of the excited state decay, both radiative and non-radiative, in solution still poses instead significant theoretical challenges.

Renewable electricity must be utilized to usefully suppress the atmospheric CO2 concentration and slow the progression of global warming. We have thus proposed a new concept involving CO2 -free electric power circulation systems via highly selective electrochemical reactions of alcohol/carboxylic acid redox couples. Design concepts for nanocatalysts able to catalyze highly selective electrochemical reactions are provided from both experimental and quantum mechanical perspectives.

In recent two years, organometal halide perovskites quantum dots are emerging as a new member of the nanocrystals family. From the chemical point of view, these perovskites quantum dots can be synthesized either by classical hot-injection technique for inorganic semiconductor quantum dots or the reprecipitation synthesis at room temperature for organic nanocrystals. From a physical point of view, the observed large exciton binding energy, well self-passivated surface, as well as the enhanced nonlinear properties have been of great interest for fundamental study. From the application point of view, these perovskites quantum dots exhibit high photoluminescence quantum yields, wide wavelength tunability and ultra-narrow band emissions, the combination of these superior optical properties and low cost fabrication makes them to be suitable candidates for display technology. In this short review, we introduce the synthesis, optical properties, the prototype light-emitting devices, and the current important research tasks of halide perovsktie quantum dots, with an emphasis on CH 3 NH 3 PbX 3 (X = Cl, Br, I) quantum dots that developed in our group.

The last five years have witnessed a huge breakthrough in the creation and the study of the properties of a new class of compounds – metamaterials. The next stage of this technological revolution will be the development of active, controllable, and non-linear metamaterials, surpassing natural media as platforms for optical data processing and quantum information applications. However, scientists are constantly faced with the need to find new methods that can ensure the formation of quantum and non-linear metamaterials with higher resolution. One such method of producing metamaterials in the future, which will provide scalability and availability, is chemical synthesis. Meanwhile, the chemical synthesis of organized 3D structures with a period of a few nanometers and a size of up to a few millimeters is not an easy task and is yet to be resolved. The most promising avenue seems to be the use of highly porous structures based on metal–organic frameworks that have demonstrated their unique properties in the field of non-linear optics (NLO) over the past three years. Thus, the aim of this review is to examine current progress and the possibilities of using metal–organic frameworks in the field of non-linear optics as chemically obtained metamaterials of the future. The review begins by presenting the theoretical principles of physical phenomena represented by mathematical descriptions for clarity. Major attention is paid to the second harmonic generation (SHG) effect. In this section we compare inorganic single crystals, which are most commonly used to study the effect in question, to organic materials, which also possess the required properties. Based on these data, we present a rationale for the possibility of studying the non-linear optical properties of metal–organic structures as well as describing the use of synthetic approaches and the difficulties associated with them. The second part of the review explicitly acquaints the reader with a new class of materials which successfully combines the positive properties of organic and inorganic materials. Using recently synthesized metal–organic frameworks and coordination polymers in the field of non-linear optics as an example, we consider synthetic approaches used for obtaining materials with desired properties and the factors to be considered in this case. Finally, probable trends towards improving the quality of the synthesized materials with regards to their further use in the field of non-linear optical effects are described.

Solar energy conversion, particularly solar-driven chemical fuel formation, has been intensely studied in the past decades as a potential approach for renewable energy generation. Efficient solar-to-fuel conversion requires artificial photosynthetic systems with strong light absorption, long-lived charge separation and efficient catalysis. Colloidal quantum confined nanoheterostructures have emerged as promising materials for this application because of the ability to tailor their properties through size, shape and composition. In particular, colloidal one-dimensional (1D) semiconductor nanorods (NRs) offer the opportunity to simultaneously maintain quantum confinement in radial dimensions for tunable light absorptions and bulk like carrier transport in the axial direction for long-distance charge separations. In addition, the versatile chemistry of colloidal NRs enables the formation of semiconductor heterojunctions (such as CdSe/CdS dot-in-rod NRs) to separate photogenerated electron–hole pairs and deposition of metallic domains to accept charges and catalyze redox reactions. In this review, we summarize research progress on colloidal NR heterostructures and their applications for solar energy conversion, emphasizing mechanistic insights into the working principle of these systems gained from spectroscopic studies. Following a brief overview of synthesis of various NRs and heterostructures, we introduce their electronic structures and dynamics of exciton and carrier transport and interfacial transfer. We discuss how these exciton and carrier dynamics are controlled by their structures and provide key mechanistic understanding on their photocatalytic performance, including the photo-reduction of a redox mediator (methyl viologen) and light driven H2 generation. We discuss the solar-driven H2 generation mechanism, key efficiency limiting steps, and potential approaches for rational improvement in semiconductor NR/metal heterostructures (such as Pt tipped CdSe@CdS dot-in-rod NRs). Finally, we conclude by pointing out challenges to be addressed in future research.

After introducing the field of Highly Frustrated Magnetism through the quest for a quantum spin liquid in dimension higher than one, we focus on the emblematic case of the kagome network. From a theoretical point of view, the simple Heisenberg case for an antiferromagnetic kagome lattice decorated with quantum spins has been a long-standing problem, not solved yet. Experimental realizations have remained scarce for long until the discovery of herbertsmithite ZnCu 3 (OH) 6 Cl 2 in 2005. This is one of the very few quantum kagome spin liquid candidates that triggered a burst of activity both on theory and experiment sides. We give a survey of theory outcomes on the “kagome” problem, review the experimental properties of that model candidate and shortly discuss them with respect to recent theoretical results.

Molecular magnetism is reaching a degree of development that will allow for the rational design of sophisticated systems. Among these, here we will focus on those that display single-molecule magnetic behaviour, i.e. classical memories, and on magnetic molecules that can be used as molecular spin qubits, the irreducible components of any quantum technology. Compared with candidates developed from physics, a major advantage of molecular spin qubits stems from the power of chemistry for the tailored and inexpensive synthesis of new systems for their experimental study; in particular, the so-called lanthanoid-based single-ion magnets, which have for a long time been one of the hottest topics in molecular magnetism. They have the potential to be chemically designed, tuning both their single-molecule properties and their crystalline environment. This allows the study of the different quantum processes that cause the loss of quantum information, collectively known as decoherence. The study of quantum decoherence processes in the solid state is necessary to answer some fundamental questions and lay the foundations for next-generation quantum technologies. This perspective article reviews the state of the art research in this field and its currently open problems.

For different classes of molecules, we have estimated from experimental data the lower limit of the height of S 1 levels for which the rule q fl + q T = 1 (q fl is the fluorescence quantum yield, q T is the quantum yield of formation of the triplet state) begins to be violated; i.e., direct nonradiative transition from the S 1-state to the ground state appears, the quantum yield of which exceeds measurement errors. We have found that, for compounds of different classes, this limit varies from 15000 to 21000 cm–1. It has been shown that the difference in the limit may be explained in terms of the inductive resonance theory of nonradiative transitions, which takes into account the localization of the electronic transition, its rate constant, and the overlap of the vibronic spectrum of the molecule with the vibrational spectrum of high-frequency vibrations taking into account the variation in the rate constant of the intersystem crossing transition to the triplet state.

In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term "giant clusters" is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.

Silicon nanocrystals (Si-NCs) are emerging as an attractive class of quantum dots owing to the natural abundance of silicon in the Earth’s crust, their low toxicity compared to many Group II–VI and III–V based quantum dots, compatibility with the existing semiconductor industry infrastructure, and their unique optoelectronic properties. Despite these favorable qualities, Si-NCs have not received the same attention as Group II–VI and III–V quantum dots, because of their lower emission quantum yields, difficulties associated with synthesizing monodisperse particles, and oxidative instability. Recent advancements indicate the surface chemistry of Si-NCs plays a key role in determining many of their properties. This Review summarizes new reports related to engineering Si-NC surfaces, synthesis of Si-NC/polymer hybrids, and their applications in sensing, diodes, catalysis, and batteries.

The Claisen rearrangement is an ideal candidate for mechanistic and transition-state analysis. Recently, physical-chemistry investigations, in particular relying on quantum mechanics and modern fs-pulse (‘short-time') laser spectroscopy, have given totally new insights here. At the same time, flow chemistry has emerged, offering considerable processing advances over batch processing. It is also known to be much powerful with inline flow sensing techniques. Yet, both key innovations have not been bridged so far and thus there is an eminent knowledge gap in mechanistic analysis of reactions. This two-review compilation is a first step to close this gap. Part 1 focuses on the insight which quantum-mechanical calculations can add to the existing knowledge based on heuristic, handy interpretation of reaction experiments in the light of electrodensity distributions. Quantum-mechanical calculation can provide geometric key data and short-time laser spectroscopy can verify this and deepen it in the sense of a comprehensive vibration analysis. In this way, prior structural assumptions can be confirmed or turned to be falsified and there is potential to resolve the uncertainty.

We review ground states and excitations of a quantum antiferromagnet on triangular and other frustrated lattices. We pay special attention to the combined effects of magnetic field h, spatial anisotropy R and spin magnitude S. The focus of the review is on the novel collinear spin density wave and spin nematic states, which are characterized by fully gapped transverse spin excitations with Sz = ± 1. We discuss extensively the R − h phase diagram of the antiferromagnet, both in the large-S semiclassical limit and the quantum S = 1/2 limit. When possible, we point out connections with experimental findings.

Strong ultrashort laser pulses have opened new avenues for the manipulation of photochemical processes like photoisomerization or photodissociation. The presence of light intense enough to reshape the potential energy surfaces may steer the dynamics of both electrons and nuclei in new directions. A controlled laser pulse, precisely defined in terms of spectrum, time and intensity, is the essential tool in this type of approach to control chemical dynamics at a microscopic level. In this Perspective we examine the current strategies developed to achieve control of chemical processes with strong laser fields, as well as recent experimental advances that demonstrate that properties like the molecular absorption spectrum, the state lifetimes, the quantum yields and the velocity distributions in photodissociation processes can be controlled by the introduction of carefully designed strong laser fields.

5,7-Dihydropyrido[3,2-b:5,6-b′]diindoles were prepared by a highly efficient two-step synthesis that involved a site-selective Suzuki coupling reaction of 2,3,5,6-tetrabromopyridine and a subsequent Pd-catalyzed cyclization that proceeded through a twofold C–N coupling reaction with aromatic and aliphatic amines. With the exception of the parent molecule, which was described in a patent without any characterization data, the 5,7-dihydropyrido[3,2-b:5,6-b′]diindoles are a new chemical entity. Their electrochemical and photochemical properties were investigated. These pyridodiindoles show promising fluorescence properties with good quantum yields and interesting electrochemical behavior. The optical and electronical properties were analyzed and explained by using DFT calculations.

In this review article, four ideas are discussed: (a) aromaticity of fullerenes patched with flowers of 6-and 8-membered rings, optimized at the HF and DFT levels of theory, in terms of HOMA and NICS criteria; (b) polybenzene networks, from construction to energetic and vibrational spectra computations; (c) quantum-mechanical calculations on the repeat units of various P-type crystal networks and (d) construction and stability evaluation, at DFTB level of theory, of some exotic allotropes of diamond D5, involved in hyper-graphenes. The overall conclusion was that several of the yet hypothetical molecular nanostructures herein described are serious candidates to the status of real molecules.

A recent review (Acevedo O, Jorgensen WL. Advances in quantum and molecular mechanical (QM/MM) simulations for organic and enzymatic reactions. Acc Chem Res 2010, 43:142–151) examined our use and development of a combined quantum and molecular mechanical (QM/MM) technique for modeling organic and enzymatic reactions. Advances included the pairwise-distance-directed Gaussian (PDDG)/PM3 semiempirical QM (SQM) method, computation of multidimensional potentials of mean force (PMF), incorporation of on-the-fly QM in Monte Carlo simulations, and a polynomial quadrature method for rapidly treating proton-transfer reactions. This article serves as a follow-up on our progress. Highlights include new reactions, alternative SQM methods, a polarizable OPLS force field, and novel solvent environments, e.g., ‘on water’ and room temperature ionic liquids. The methodology is strikingly accurate across a wide range of condensed-phase and antibody-catalyzed reactions including substitution, decarboxylation, elimination, isomerization, and pericyclic classes. Comparisons are made to systems treated with continuum-based solvents and ab initio or density functional theory (DFT) methods. Overall, the QM/MM methodology provides detailed characterization of reaction paths, proper configurational sampling, several advantages over implicit solvent models, and a reasonable computational cost. WIREs Comput Mol Sci 2014, 4:422–435. Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

This article discusses the existing methods to correlate NMR parameters describing the high resolution NMR spectra of liquids and solid systems with their structural parameters. Those methods are divided into direct and indirect ones. This article includes two types of direct methods: those based on the Nuclear Overhauser Effect (NOE) contributions to the NMR relaxation and those based on direct measurements of the dipolar couplings using several experimental approaches. Indirect methods are based on the intrinsic dependence of J couplings and shieldings on the atomic coordinates of the atoms in a molecule and its surroundings, requiring complex quantum mechanical calculations to relate NMR spectral properties to molecular and crystal structure. This article discusses how changes in chemical bonding, conformation, and stereo configurations that cause measurable changes in NMR parameters closely related to molecular and crystal structure. The final section provides information about the software and hardware required to perform calculations needed to solve structural problems using high resolution NMR. This article intends to provide molecular structural researchers new to the field of NMR, with an overall panorama of the potential of using high resolution NMR for structure elucidation, when other more traditional techniques are not feasible. To this end and to emphasize the didactic value of this work, after each section a brief conclusion has been added to recap the critical concepts. © 2014 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 261–289, 2013.

ConspectusConsiderable effort in the past decade has been extended toward achieving computationally affordable theoretical methods for accurate prediction of the structure and properties of materials. Theoretical predictions of solids began decades ago, but only recently have solid-state quantum techniques become sufficiently reliable to be routinely chosen for investigation of solids as quantum chemistry techniques are for isolated molecules. Of great interest are ab initio predictive theories for solids that can provide atomic scale insights into properties of bulk materials, interfaces, and nanostructures. Adaption of the quantum chemical framework is challenging in that no single theory exists that provides prediction of all observables for every material type. However, through a combination of interdisciplinary efforts, a richly textured and substantive portfolio of methods is developing, which promise quantitative predictions of materials and device properties as well as associated performance analy...

ConspectusChemistry, particularly organic chemistry, is mostly concerned with functional groups: amines, amides, alcohols, ketones, and so forth. This is because the reactivity of molecules can be categorized in terms of the reactions of these functional groups, and by the influence of other adjacent groups in the molecule. These simple truths ought to be reflected in the electronic structure and electronic energy of molecules, as reactivity is determined by electronic structure. However, sophisticated ab initio quantum calculations of the molecular electronic energy usually do not make these truths apparent. In recent years, several computational chemistry groups have discovered methods for estimating the electronic energy as a sum of the energies of small molecular fragments, or small sets of groups. By decomposing molecules into such fragments of adjacent functional groups, researchers can estimate the electronic energy to chemical accuracy; not just qualitative trends, but accurate enough to understan...

Adetailed understanding of the action of biological molecules is a pre-requisite for rational advances in health sciences and related fields. Here, the challenge is to move from available structural information to a clear understanding of the underlying function of the system. In light of the complexity of macromolecular complexes, it is essential to use computer simulations to describe how the molecular forces are related to a given function. However, using a full and reliable quantum mechanical representation of large molecular systems has been practically impossible. The solution to this (and related) problems has emerged from the realization that large systems can be spatially divided into a region where the quantum mechanical description is essential (e.g. a region where bonds are being broken), with the remainder of the system being represented on a simpler level by empirical force fields. This idea has been particularly effective in the development of the combined quantum mechanics/molecular mechanics (QM/MM) models. Here, the coupling between the electrostatic effects of the quantum and classical subsystems has been a key to the advances in describing the functions of enzymes and other biological molecules. The same idea of representing complex systems in different resolutions in both time and length scales has been found to be very useful in modeling the action of complex systems. In such cases, starting with coarse grained (CG) representations that were originally found to be very useful in simulating protein folding, and augmenting them with a focus on electrostatic energies, has led to models that are particularly effective in probing the action of molecular machines. The same multiscale idea is likely to play a major role in modeling of even more complex systems, including cells and collections of cells.

The first gas-phase high-resolution FTIR spectra of S2N2 (D2h) is presented together with a high-level quantum mechanical and experimental study of its molecular ground-state and equilibrium structures.

Powder samples of the title Zintl phase are obtained from a stoichiometric mixture of Cs4Si4 and Na4Si4 (Ta ampule, 500 °C, 14 d).

Transition metals nanoalloys are emerging as an important multidisciplinary field with increasing impact throughout nanoscience and technology. Many body phenomena like magnetism are particularly interesting in this context since, as a result of their quantum mechanical nature, they are very sensitive to the local and chemical environment of the atoms. The microscopic understanding of the trends governing the properties of these binary nanoparticles constitutes an important step towards quantum-based magnetic nanoalloy design. Their novel electronic and magnetic properties should open a wide range of potential applications, e.g., in high-density recording, spintronics or biomedicine. In view of applications, the magnetic anisotropy energy plays a particularly important role. In this contribution, we first review the MAE of CoxRh1x nanoalloys in order to disclose their dependence on relevant parameters like composition, size and chemical order. Second, we discuss the possibility of tailoring giant MAE by a...

Nitrogen-vacancy (NV) centers in diamond have recently emerged as a unique platform for fundamental studies in quantum information and nanoscience. The special properties of these impurity centers allow robust, room-temperature operation of solid-state qubits and have enabled several remarkable demonstrations in quantum information processing and precision nanoscale sensing. This article reviews the recent advances in magnetic and optical manipulation of the NV center’s quantum spin and their importance for prospective applications. We discuss how quantum control of individual centers can be harnessed for the protection of NV-center spin coherence, for multiqubit quantum operations in the presence of decoherence, and for high-fidelity initialization and readout. We also discuss the progress in resonant optical control, which has led to interfaces between spin and photonic qubits and may lead to spin networks based on diamond photonics. Many of these recently developed diamond-based technologies constitute...

Computational chemistry deals with the first-principles calculation of electronic and crystal structures, phase diagrams, charge distributions, vibrational frequencies, or ion diffusivity in complex molecules and solids. Typically, none of these numerical experiments allows for the calculation of electrical currents under the influence of externally applied voltages. To address this issue, there is an imperative need for an advanced simulation approach capable of treating all kind of transport phenomena (electron, energy, momentum) at a quantum mechanical level. The goal of this tutorial review is to give an overview of the “quantum transport” (QT) research activity, introduce specific techniques such as the Non-equilibrium Green's Function (NEGF) formalism, describe their basic features, and underline their strengths and weaknesses. Three examples from the nanoelectronics field have been selected to illustrate the insight provided by quantum transport simulations. Details are also given about the numerical algorithms to solve the NEGF equations and about strategies to parallelize the workload on supercomputers.

Magnetic clusters, i.e., assemblies of a finite number (between two or three and several hundred) of interacting spin centers which are magnetically decoupled from their environment, can be found in many materials ranging from inorganic compounds, magnetic molecules, artificial metal structures formed on surfaces to metalloproteins. The magnetic excitation spectra in them are determined by the nature of the spin centers, the nature of the magnetic interactions, and the particular arrangement of the mutual interaction paths between the spin centers. Small clusters of up to four magnetic ions are ideal model systems to examine the fundamental magnetic interactions which are usually dominated by Heisenberg exchange, but often complemented by anisotropic and/or higher-order interactions. In large magnetic clusters which may potentially deal with a dozen or more spin centers, the possibility of novel many-body quantum states and quantum phenomena are in focus. In this review the necessary theoretical concepts and experimental techniques to study the magnetic cluster excitations and the resulting characteristic magnetic properties are introduced, followed by examples of small clusters demonstrating the enormous amount of detailed physical information which can be retrieved. The current understanding of the excitations and their physical interpretation in the molecular nanomagnets which represent large magnetic clusters is then presented, with an own section devoted to the subclass of the single-molecule magnets which are distinguished by displaying quantum tunneling of the magnetization. Finally, some quantum many-body states are summarized which evolve in magnetic insulators characterized by built-in or field-induced magnetic clusters. The review concludes addressing future perspectives in the field of magnetic cluster excitations.

Strongly correlated electron systems at the border of magnetism are of active current interest, particularly because the accompanying quantum criticality provides a route towards both strange-metal non-Fermi liquid behavior and unconventional superconductivity. Among the many important questions is whether the magnetism acts simply as a source of fluctuations in the textbook Landau framework, or instead serves as a proxy for some unexpected new physics. We put into this general context the recent developments on quantum phase transitions in antiferromagnetic (AF) heavy fermion metals. Among these are the extensive recent theoretical and experimental studies on the physics of Kondo destruction in a class of beyond-Landau quantum critical points (QCPs). Also discussed are the theoretical basis for a global phase diagram of AF heavy fermion metals, and the recent surge of materials suitable for studying this phase diagram. Furthermore, we address the generalization of this global phase diagram to the case of Kondo insulators, and consider the future prospect to study the interplay among Kondo coherence, magnetism, and topological states. Finally, we touch upon related issues beyond the AF settings, arising in mixed valent, ferromagnetic, quadrupolar, or spin glass f-electron systems, as well as some general issues on emergent phases near QCPs.

Rational design of molecules and materials usually requires extensive screening of molecular structures for the desired property. The inverse approach to deduce a structure for a predefined property would be highly desirable, but is, unfortunately, not well defined. However, feasible strategies for such an inverse design process may be successfully developed for specific purposes. We discuss options for calculating “jacket” potentials that fulfill a predefined target requirement—a concept that we recently introduced (Weymuth and Reiher, MRS Proceedings 2013, 1524, DOI:10.1557/opl.2012.1764). We consider the case of small-molecule activating transition metal catalysts. As a target requirement we choose the vanishing geometry gradients on all atoms of a subsystem consisting of a metal center binding the small molecule to be activated. The jacket potential can be represented within a full quantum model or by a sequence of approximations of which a field of electrostatic point charges is the simplest. In a second step, the jacket potential needs to be replaced by a chemically viable chelate-ligand structure for which the geometry gradients on all of its atoms are also required to vanish. To analyze the feasibility of this approach, we dissect a known dinitrogen-fixating catalyst to study possible design strategies that must eventually produce the known catalyst. © 2014 Wiley Periodicals, Inc.

Sideband patterns in single quantum and double quantum magic angle spinning NMR spectra are reviewed. Their use in elucidating non-covalent interactions, such as hydrogen bonds or pi-pi stacking, is demonstrated by studies of supramolecular systems of current interest. Moreover, the effects of local and collective motions are illustrated by examples from supramolecular and macromolecular science.

This article reviews the unconventional effects of random disorder on magnetic quantum phase transitions, focusing on a number of new experimental and theoretical developments during the last three years. On the theory side, we address smeared quantum phase transitions tuned by changing the chemical composition, for example in alloys of the type A1−xBx. We also discuss how the interplay of order parameter conservation and overdamped dynamics leads to enhanced quantum Griffiths singularities in disordered metallic ferromagnets. Finally, we discuss a semiclassical theory of transport properties in quantum Griffiths phases. Experimental examples include the ruthenates Sr1−xCaxRuO3 and (Sr1−xCax)3Ru2O7 as well as Ba(Fe1−xMnx)2As2.

This article reviews some of our recent progress on materials design guidelines for photoinduced charge generation in bulk-heterojunction organic solar cells. Over the last 7 years, our group has employed transient absorption measurement to determine the relative quantum yields of long-lived polaron pairs for over 300 different organic Donor/Acceptor blend films. We have shown that this optical assay of charge separation can be a strong indicator of photocurrent generation efficiency in complete devices. In this review, we consider the lessons that can be drawn from these studies concerning the parameters that determine efficiency of this photoinduced charge separation in such solar cells. We consistently find, from studies of several materials series, that the energy offset driving charge separation is a key determinant of the efficiency of this charge generation, and thereby photocurrent generation. Moreover, we find that the magnitude of the energy offset required to drive charge separation, and the st...

We describe a new class of ligands for semiconductor nanoparticles (quantum dots = QDs), which bind well and allow for their facile dissolution in aqueous solution. As a proof of principle, we have designed and synthesized a novel bis(phosphine)-modified peptide (BPMP) and shown that it has the ability to solubilize quantum dots in aqueous media. We further showed that the corresponding phosphine oxide derivatives of these new ligands are less good at solubilizing the quantum dots. These new bis(phosphine)-modified peptide ligands are easy to prepare and may well replace thiol-containing binding sequences in functionalized peptides for quantum dot coating, potentially resulting in quantum dots with higher quantum yields.

Chiroptical spectroscopy utilizing left- and right-handed electromagnetic fields has been used to obtain stereochemical information on chiral molecules in condensed phases. However, due to weak signals (10−6 to 10−2 of absorption), not only are accurate measurements of chiroptical signals difficult but also preferential excitation of one type of handed molecule over the other using chiral fields (i.e., optical enantioselectivity) is limited. Recently, methods have been developed to enhance chiroptical signals and optical enantioselectivity by properly controlling polarization states, designing detection schemes, and modifying spatial properties of chiral fields. In the physics community, similar enhancements have been introduced using a quantum mechanical theory called “weak value measurement.” Here we provide examples of these techniques, corresponding enhancement mechanisms, and more importantly connections between them.

Stable colloids of disk-shaped hexagonal Cu2Te nanocrystals are prepared by injecting a trioctylphosphine/Te (3:1) solution into solution of Cu(acac)2 1-octanethiol, and oleic acid (1.

Microwave photons trapped in a superconducting cavity constitute an ideal system to realize some of the thought experiments imagined by the founding fathers of quantum physics. The interaction of these trapped photons with Rydberg atoms crossing the cavity illustrates fundamental aspects of measurement theory. The experiments performed with this "photon box" at Ecole Normale Superieure (ENS) belong to the domain of quantum optics called "Cavity Quantum Electrodynamics". We have realized the non-destructive counting of photons, the recording of field quantum jumps, the preparation and reconstruction of "Schrodinger cat" states of radiation and the study of their decoherence, which provides a striking illustration of the transition from the quantum to the classical world. These experiments have also led to the demonstration of basic steps in quantum information processing, including the deterministic entanglement of atoms and the realization of quantum gates using atoms and photons as quantum bits. This lecture starts by an introduction stressing the connection between the ENS photon box and the ion trap experiments of David Wineland, whose accompanying lecture recalls his own contribution to the field of single particle control. I give then a personal account of the early days of Cavity Quantum Electrodynamics before describing the main experiments performed at ENS during the last twenty years and concluding by a discussion comparing our work to other researches dealing with the control of single quantum particles.

We present an overview of unconventional phenomena arising close to ferromagnetic and ferroelectric quantum phase transitions. The applicability and potential breakdown of traditional field theories of quantum criticality and the emergence of a multiplicity of critical fields in particular will be discussed.

One of the most surprising and significant advances in the study of the photosynthetic light-harvesting process is the discovery that the electronic energy transfer might involve long-lived electronic coherences, under physiologically relevant conditions. This means that the transfer of energy among different chromophores does not follow the expected classical incoherent hopping mechanism, but that quantum-mechanical laws can steer the migration of energy. The implications of such a quantum transport regime, although currently under debate, might have a tremendous impact on our way of thinking about natural and artificial light-harvesting. Central to these discoveries has been the development of new ultrafast spectroscopic techniques, in particular two-dimensional electronic spectroscopy, which is now the primary tool to obtain clear and definitive experimental proof of such effects. This review aims to provide an overview of the experimental techniques developed with the purpose of attaining a more detailed picture of the coherent and incoherent quantum dynamics relevant to energy transfer processes, not limited to the two-dimensional electronic spectroscopy. With the idea of summarizing the experimental and theoretical basic notions necessary to introduce the field, the connection between experimental observables and coherence dynamics will be analysed in detail for each technique, highlighting how electronic coherences could be manifested in different experimental signatures. Similarities and differences among coherent signals as well as advantages and disadvantages of each approach will be critically discussed. Current opinions and debated issues will be emphasised and some possible future directions to address still open questions will be suggested.

The prospect of designing novel materials with electrical, optical, and magnetic properties by design has intrigued scientists and engineers for years. Building blocks for such “artificial solids” have emerged from recent advances in nanomaterial synthesis, characterization, and emerging understanding of their size-dependent properties. Colloidal semiconductor nanocrystal quantum dots (NQDs) stand out as an intellectually intriguing and experimentally advantageous system for the fundamental study of artificial solids and their technological development. The authors review the rapid evolution of artificial solids from an early theoretical concept towards the refined control of metamaterials with programmable electronic structure and their potential commercial applications, in particular, in next-generation energy technologies. The review is organized around the three independently adjustable parameters of artificial solids: (i) the electronic structure of NQD as artificial atom by tailoring the quantum con...

We give an overview on experimental studies performed in the last 25 years on heavy-fermion systems in a high magnetic field. The properties of field-induced magnetic transitions in heavy-fermion materials close to a quantum antiferromagnetic-to-paramagnetic instability are presented. Effects of a high magnetic field to the Fermi surface, in particular the splitting of spin-up and spin-down bands, are also considered. Finally, we review on recent advances on the study of non-centrosymmetric compounds and ferromagnetic superconductors in a high magnetic field.

We review the theoretical and the experimental researches aimed at quantifying or identifying quantum correlations in liquid-state nuclear magnetic resonance (NMR) systems at room temperature. We first overview, at the formal level, a method to determine the quantum discord and its classical counterpart in systems described by a deviation matrix. Next, we describe an experimental implementation of that method. Previous theoretical analysis of quantum discord decoherence had predicted the time dependence of the discord to change suddenly under the influence of phase noise. The experiment attests to the robustness of the effect, sufficient to confirm the theoretical prediction even under the additional influence of a thermal environment. Finally, we discuss an observable witness for the quantumness of correlations in two-qubit systems and its first NMR implementation. Should the nature, not the amount, of the correlation be under scrutiny, the witness offers the most attractive alternative.

In recent years polynuclear transition metal molecules have been synthesized and proposed for example as magnetic storage units or qubits in quantum computers. They are known as molecular nanomagnets and belong in the class of mesoscopic systems, which are large enough to display many-body effects but small enough to be away from the finite-size scaling regime. It is a challenge for physicists to understand their magnetic properties, and for synthetic chemists to efficiently tailor them by assembling fundamental units. They are complementary to artificially engineered spin systems for surface deposition, as they support a wider variety of complex states in their low energy spectrum. Here a few characteristic examples of molecular nanomagnets showcasing unusual many-body effects are presented. Antiferromagnetic wheels and chains can be described in classical terms for small sizes and large spins to a great extent, even though their wavefunctions do not significantly overlap with semiclassical configurations. Hence, surprisingly, for them the transition from the classical to the quantum regime is blurred. A specific example is the Fe18 wheel, which displays quantum phase interference by allowing Neel vector tunneling in a magnetic field. Finally, the Co5Cl single-molecule magnet is shown to have an unusual anisotropic response to a magnetic field.

We review two possible geometrically frustrated lattices among itinerant electron magnets. One is a dimer‐bridged octahedral lattice found in Mo3Sb7, where frustration‐induced lattice instability has been observed. Another is the stella quadrangula lattice found in η‐carbide‐type compounds. The quantum critical behavior observed in Fe3Mo3N is discussed in connection with the unique frustration expected in the stella quadrangula lattice.

The number of permitted single quantum (SQ) transitions in the 1H NMR spectra of scalar-coupled spins increases rapidly with the increase in the number of interacting spins, thereby posing a challenge for their analyses. The numerous two-dimensional methodologies are available in the knowledge bank of NMR for the determination of spectral parameters and to obtain information on the molecular structure and conformation. The indirect detection of forbidden higher quantum NMR transitions, that is, other than those allowed by the normal selection rules for the detection of SQ frequencies, is one of the significant steps in this direction. The detection of higher quantum transitions of coupled spin 1/2 nuclei has been extensively employed for the study of molecules oriented in strong and weak aligning media, not only to simplify the analyses of complex NMR spectra but also to determine the molecular geometries. In this chapter, we discuss our recent studies on the development and applications of higher quantum correlation and resolved techniques for the analyses of complex 1H NMR spectra of scalar-coupled spins. The behaviour of magnetization in the spin-selected and non-selected higher quantum is discussed using both product operator and polarization operator approaches for a weakly coupled AMX spin system. Subsequently, applications of these methodologies for the analyses of complex 1H NMR spectra have been discussed with specific examples.