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The energy profiles of hydrogen-bonded heterocyclic aromatics have been decomposed into atomistic energy contributions using the Interacting Quantum Atoms (IQA) method. The resulting energy contributions have been sequenced by the Relative Energy Gradient (REG) approach in order to determine their influence upon the shape of these energy profiles. The results show inadequacies in Jorgensen’s secondary interaction hypothesis (SIH). A novel method of finding a condensed analogy for the interaction between the molecules is presented. The findings of this work further doubt the validity of the SIH, and reinforce previous warnings against its misguided use.

This work concerns the typical conformational behaviors for di-substituted cyclohexanes that inherently depend on spatial orientations of side chains in flexible cyclic ring. The 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane in both cis- and trans-configurations were focused here to unravel their conformational inversion-topomerization mechanisms. Full geometry optimizations were performed at B3LYP/6-311++G(d,p) level of theory to explicitly identify all distinguishable molecular structures, and thus explore potential energy surfaces (PES) of the complete interconversion routes for two stereoisomers of 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane. Additional quantum calculations were carried out by separately applying MP2/6-311++G(d,p), G4, and CCSD(T)/6-311++G(d,p) methods to further refine all PES’ stationary points. With respect to quantum results, the conformational analysis was conducted to gain insight into the determination, thermodynamic stabilities, and relative energies of distinct molecular geometric structures. On base of highly biased conformational equilibria, the temperature-dependent populations of stable local minima for four studied dimethylcyclohexanes were obtained by utilizing Boltzmann distribution within 300-2500 K. Moreover, two unique interconversion processes for them, including inversion and topomerization, were fully investigated, and their potential energy surfaces were illustrated with the rigorous descriptions in two or three-dimensional schemes for clarify.

2030-12-30 The structural, electronic, and vibrational properties of two leading representatives of the Zn-based spinel oxides class, normal ZnX2O4 (X = Al, Ga, In) and inverse Zn2MO4 (M = Si, Ge, Sn) crystals, were investigated. In particular, density functional theory (DFT) was combined with different exchange-correlation functionals: B3LYP, HSE06, PBE0, and PBESol. Our calculations showed good agreement with the avail- able experimental data, showing a mean percentage error close to 3% for structural parameters. For the electronic structure, the obtained HSE06 band-gap values overcome previous theoretical results, exhibiting a mean percentage error smaller than 10.0%. In particular, the vibrational properties identify the significant differences between normal and inverse spinel configurations, offering compelling evidence of a structure-property relationship for the investigated materials. Therefore, the combined results confirm that the range-separated HSE06 hybrid functional performs the best in spinel oxides. Despite some points that cannot be directly compared to experimental results, we expect that future experimental work can confirm our predictions, thus opening a new avenue for understanding the structural, electronic, and vibrational properties in spinel oxides

In this contribution we review in a rigorous, yet comprehensive fashion the assessment of the one-body reduced density matrices derived from the most used single-reference excited-state calculation methods in the framework of the equation-of-motion formalism. Those methods are separated into two types: those which involve the coupling of a deexcitation operator to a single-excitation transition operator, and those which do not involve such a coupling. The case of many-body auxiliary wave functions for excited states is also addressed. For each of these approaches we were interested in deriving the elements of the one-body transition and difference density matrices, and to highlight their particular structure. This has been accomplished by applying a decomposition of integrals involving one-determinant quantum electronic states on which two or three pairs of second quantization operators can act. Such a decomposition has been done according to a corollary to Wick's theorem, which is brought in a comprehensive and detailed manner. A comment is also given about the consequences of using the equation-of-motion formulation in this context, and the two types of excited-state calculation methods (with and without coupling excitations to deexcitations) are finally compared from the point of view of the structure of their transition and difference density matrices.

Unique properties of lead chalcogenides have enabled multiple exciton generation (MEG) in their nanocrystals that can be beneficial in enhancing the efficiency of third-generation solar cells. Although the intrinsic electric field plays an imperative role in a solar cell, its effect on the multiple exciton generation (MEG) has been overlooked, so far. Using EOM-CCSD as a many-body approach, we show that any electric field can affect the absorptivity spectra of the lead chalcogenide nanocrystals (Pb4 Te4 , Pb4 Se4 , and Pb4 S4 ). The same electric field, however, has insignificant effects on the MEG quantum probabilities and the thresholds in these nanocrystals. Furthermore, simulations show that Pb4 Te4 , among the aforementioned nanocrystals, has the lowest MEG threshold and the strongest absorptivity peak that is located in the multi-excitation window, irrespective of the field strength, making it the most suitable candidate for MEG applications. Simulations also demonstrate that an electric field affects the MEG characteristics in the Pb4 Te4 nanocrystal, in general, less than it perturbs MEG characteristics in Pb4 Se4 and Pb4 S4 nanocrystals. Our results can have a great impact in designing optoelectronic devices whose performance can be significantly influenced by MEG.

International audience; Increasing fluorescence quantum yields of ligand-protected gold nanoclusters has attracted wide research interest. The strategy consisting in using bulky counterions has been found to dramatically enhance the fluorescence. In this communication, we push forward this concept to the nonlinear optical regime. We show that by an appropriate choice of bulky counterions and of solvent, a 30-fold increase in two-photon excited fluorescence (TPEF) signal at ~600 nm for gold nanoclusters can be obtained. This would correspond to a TPEF cross section in the range of 0.1 to 1 GM. The quest for high resolutions and penetration depths with spectroscopic tools has led to innovative approaches in optical microscopy of biological systems. Two-photon excited fluorescence (TPEF) microscopy is probably the most important advance in optical microscopy of biological systems since the introduction of confocal imaging. 1 The successful application of TPEF is partly due to the fact that commonly used fluorescent molecules can be efficiently excited by the simultaneous absorption of 2 photons. 2, 3 However, to reach ultrahigh detection sensitivity, newly engineered nonlinear optical (NLO) chromophores, endowed with large two-photon absorption cross-sections, have to be developed. Liganded silver and gold quantum clusters represent a promising direction in the quest to develop novel nonlinear optical nanomaterials. Pioneering studies have clearly demonstrated that ligated noble metal nanoclusters (NCs), with few to hundred atoms exhibit remarkable optical nonlinearities. 4-6 Shortly afterwards, strong two-photon emission was reported from uncharacterized gold clusters, making them a promising alternative as contrast agents for live cells imaging. 7 Thus, these ligated nanoclusters may provide a valuable route within the nonlinear optical regime. We have described in our combined experimental and theoretical investigations how to improve two-photon absorption (TPA) properties in such quantum nanoclusters, through the concept of "ligand-core" NLO-phores. 8 The structure of the metallic core, its charge and symmetry (influencing the NLO cross sections), and the ligands stabilizing the core play a major role in TPA efficiencies. 9 However, the main conclusion so far is that liganded silver and gold quantum clusters are excellent two-photon absorbers but are rather poor two-photon excited emitters. 10 For example, the two-photon absorption cross-section at 780 nm for Au15 is ~65 700 GM, while its TPEF cross section at 475 nm is only ~0.022 GM. 11 Concerning nonlinear emissive properties, both experimental and theoretical progresses are needed in order to produce not only large TPA but also large TPEF cross sections. On the one hand, alloying is a promising strategy. Indeed, Le Guével et al 12 reported enhanced fluorescence of gold nanoclusters by silver doping. Likewise, two-photon excited fluorescence emission was also found to be enhanced. 13 Unfortunately, the exact stoichiometry of such AuAg nanoclusters remains unknown and has prevented the report of any quantitative estimation of TPEF cross-sections. On the other hand, it is well known that the ligand shell rigidity 14, 15 influences the emissive properties of Au NCs. A simple way to increase rigidity of the protective shell is to use as ligands proteins instead of thiolated molecules. Xie et al. 16 have developed a facile, one-pot, "green" synthetic technique based on bovine serum albumin (BSA). It was shown that BSA-Au25 clusters also exhibit an efficient two photon absorption followed by red to near-infrared luminescence. 17 However, no two photon absorption cross section was reported due to the difficulty in calculating the precise concentration of the clusters in the solution. Using (bio)organic thiolate templates, further enhancement can be achieved by the increased rigidity of the metal-thiolate shell. Pyo et al. 18 have shown that it is possible to achieve one-photon excited luminescence quantum yields >60% by rigidifying the gold shell with the binding of bulky groups (e.g. tetraoctylammonium (TOA) cations). In this communication, we push forward this concept to the nonlinear optical regime. We show that by an appropriate choice of bulky counterions and solvents, a dramatic enhancement of TPEF cross sections for Au15(SG)13 and Au18(SG)14 can be obtained. [a] Dr.

International audience; Herein, we discuss three methods to partition the total molecular energy into additive atomic contributions within the framework of Bader's atoms‐in‐molecules theory and in the particular context of Kohn–Sham density functional theory. The first method is derived from the virial theorem, whereas the two other schemes, termed “standard” and “model”, are based on Pendás’ interacting‐quantum‐atoms decomposition. The methods are then compared for a dataset of molecules of interest for direct application in organic chemistry and biochemistry. Finally, the relevance of the three methods for the prediction of intrinsic reactivity properties (e.g., electrophilicity) or for unravelling the nature of chemical bonding (e.g., in halogen bonds, beyond the pure electrostatic point of view), is examined and paves the way for their more systematic use for the in silico design of new reactants.

The reliable calculation of the excited states of charge-transfer (CT) compounds poses a major challenge to the ab initio community because the frequently employed method, time-dependent density functional theory (TD-DFT), massively relies on the underlying density functional, resulting in heavily Hartree-Fock (HF) exchange-dependent excited-state energies. By applying the highly sophisticated many-body perturbation approach, we address the encountered unreliabilities and inconsistencies of not optimally tuned (standard) TD-DFT regarding photo-excited CT phenomena, and present results concerning accurate vertical transition energies and the correct energetic ordering of the CT and the first visible singlet state of a recently synthesized thermodynamically stable large hybrid perylene bisimide-macrocycle complex. This is a large-scale application of the quantum many-body perturbation approach to a chemically relevant CT system, demonstrating the system-size independence of the quality of the many-body-based excitation energies. Furthermore, an optimal tuning of the ωB97X hybrid functional can well reproduce the many-body results, making TD-DFT a suitable choice but at the expense of introducing a range-separation parameter, which needs to be optimally tuned.

This investigation uses atomic properties derived from the quantum theory of atoms in molecules formalism to rationalize the infrared intensity of the stretching vibration that arises as a Lewis base (B) is protonated (B-H mode). Moreover, the interacting quantum atom (IQA) partition is employed to evaluate the energetics of protonation. All calculations are performed at the CCSD/cc-pVQZ level except by the IQA analysis, which is carried out by means of the B3LYP/cc-pVQZ//CCSD/cc-pVQZ treatment. First, an efficiency scale is established for Lewis bases in terms of the electronic charge transfer potential. Next, this study shows that the intensity of the B-H stretching depends mostly on the electronic charge amount transferred to the proton. Thus, intensity data provide empirical assessment of Lewis base charge transfer efficiency. Finally, the group separation observed during correlation of proton affinities and electronic charge transfer potential is explained by the interaction energy between fragments of the protonated system.

In this reply we clarify questions point out in the Comment on: “The Effect of Confinement on the Electronic Energy and Polarizability of a Hydrogen Molecular Ion” by J. F. da Silva, F. R. Silva and E. Drigo Filho, Int. J. Quantum Chem.2016, 116, 497–503 written by S. A. Cruz and H. Olivares-Pilon. In particular, we show how we made the calculations of ground state energy from the confined hydrogen molecule ion for cavities of different volumes. The internuclear distances to the excited state 2pσu are also presented.

A very promising recent trend in applied quantum physics is to combine the advantageous features of different quantum systems into what is called "hybrid quantum technology". One of the key elements in this new field will have to be a quantum memory enabling to store quanta over extended periods of time. Systems that may fulfill the demands of such applications are comb-shaped spin ensembles coupled to a cavity. Due to the decoherence induced by the inhomogeneous ensemble broadening, the storage time of these quantum memories is, however, still rather limited. Here we demonstrate how to overcome this problem by burning well-placed holes into the spectral spin density leading to spectacular performance in the multimode regime. Specifically, we show how an initial excitation of the ensemble leads to the emission of more than a hundred well-separated photon pulses with a decay rate significantly below the fundamental limit of the recently proposed "cavity protection effect".

Achieving low-threshold optical gain for solution-processed materials is crucial for their real-life applications and deployment as gain media. However, the realization of low gain threshold in the blue region has shown to be technically an extremely challenging task using colloidal nanocrystals as a result of fast nonradiative Auger rates in smaller nanocrystals. Here, ultralow-threshold blue amplified spontaneous emission (ASE) (≈2.7 µJ cm ) accompanied with a large net modal gain coefficient of 360 cm in the blue enabled by blue-emitting (≈455–465 nm) colloidal quantum rings (QRs) of inverted type-I CdS/CdSe core/crown nanoplatelets (NPLs) is proposed and demonstrated. The synthesized QRs with controlled crown size outperform the best reported ASE thresholds and net modal gain coefficients from the solution-processed materials by ≈2.5- and ≈4-fold, respectively, in the similar blue spectral window. Utilizing this QR architecture, it is also shown that the ASE peak can be spectrally tuned by controlling the lateral size of the crown and hence quantum confinement in the lateral direction. These outstanding results support the prospects of these solution-processed QRs made of 2D hetero-NPLs in the challenging blue region as colloidal gain. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Accepted version

This work was partially supported by NSF CMMI-1562057 and ECCS-1807463. The authors appreciate Dr. Lingmei Liu and Prof. Yu Han at KAUST for helpful suggestions on TEM characterization.

The recent progress in integrated quantum optics has set the stage for the development of an integrated platform for quantum information processing with photons, with potential applications in quantum simulation. Among the different material platforms being investigated, direct-bandgap semiconductors and particularly gallium arsenide (GaAs) offer the widest range of functionalities, including single- and entangled-photon generation by radiative recombination, low-loss routing, electro-optic modulation and single-photon detection. This paper reviews the recent progress in the development of the key building blocks for GaAs quantum photonics and the perspectives for their full integration in a fully-functional and densely integrated quantum photonic circuit.

Albeit its chemical inertness, rare gas doping can substantially enhance the quantum size effect of nanocrystals, yet little attention has been paid on this fascination and the mechanism behind remains unclear. Here, we show that the rare gas dopant breaks bonds of its neighboring atoms, which effects the same to atomic under-coordination on the bond strain, energy quantum entrapment, and valence electron polarization of Li and Na clusters. Consistency between density functional theory calculation and the bond-order-length-strength correlation prediction revealed that the bond strain by 16.86% and 21.12% before and after He doping for Na30 clusters. Observations suggest an effective yet simple means to modulate the physical properties by doping the inert gases.

A quantum-classical transition equation in complex space is derived in the framework of the complex quantum Hamilton–Jacobi formalism. The transition equation is obtained by subtracting a complex-valued quantum potential term from the complex-extended time-dependent Schrodinger equation (TDSE). It is shown that the nonlinear transition equation is equivalent to a linear scaled TDSE with a rescaled Planck's constant. Employing the quantum momentum function defined by the gradient of the complex action, we can analyze the quantum-classical transition of physical systems using complex transition trajectories. Complex transition trajectories are presented for the free Gaussian wave packet, the harmonic oscillator, and the Morse potential. This study demonstrates that the transition equation provides a continuous description for the quantum-classical transition of physical systems in complex space.

In this review, the origins of astrochemistry and the initial applications of quantum chemistry to the discovery of new molecules in space are discussed. Furthermore, more recent successes and failures of quantum astrochemistry are explored. Finally, the application of quantum chemistry to the chemical study of space is driving developments in large-scale computational science. Consequently, cloud computing and large molecule computations are discussed. Astrochemistry is a natural application of quantum chemistry. The ability to analyze routinely and completely the structural, spectroscopic, and electronic properties of any given molecule, regardless of its laboratory stability, make this tool a necessary component for astrochemical analysis. The sizes of the computations scaling with the number of electrons and degrees-of-freedom can become limiting, but proper choices of methods can provide unique insights. The chemistry of the Earth is a small snapshot of the chemistries available in the universe at large, and the flexibility inherent within computation make quantum chemistry an excellent driver of new knowledge in fundamental molecular science as well as in astrophysics. © 2016 Wiley Periodicals, Inc.

Granting information privacy is of crucial importance in our society, notably in fiber communication networks. Quantum cryptography provides a unique means to establish, at remote locations, identical strings of genuine random bits, with a level of secrecy unattainable using classical resources. However, several constraints, such as non-optimized photon number statistics and resources, detectors' noise, and optical losses, currently limit the performances in terms of both achievable secret key rates and distances. Here, these issues are addressed using an approach that combines both fundamental and off-the-shelves technological resources. High-quality bipartite photonic entanglement is distributed over a 150 km fiber link, exploiting a wavelength demultiplexing strategy implemented at the end-user locations. It is shown how coincidence rates scale linearly with the number of employed telecommunication channels, with values outperforming previous realizations by almost one order of magnitude. Thanks to its potential of scalability and compliance with device-independent strategies, this system is ready for real quantum applications, notably entanglement-based quantum cryptography.

Quantum mechanical exchange effects in purely organic N,N′-dioxy-2,6-diazaadamantane biradical derivatives with promesogenic substituents have been studied. To determine intermolecular exchange energies, packing conditions of the radical core units in layered liquid crystalline phases are simulated using the Gaussian 09 program. The broken symmetry approach gives J ≈ 7 cm−1 for intramolecular ferromagnetic exchange interactions between nitroxyl radical centers in one molecule. Both ferromagnetic and antiferromagnetic intermolecular interactions are possible in this kind of systems according to the obtained calculation results. Depending on the mutual positioning and orientation of molecules, the intermolecular antiferromagnetic exchange constant can reach a value of −50 cm−1, and the intermolecular ferromagnetic constant a value of 10 cm−1. The simultaneous presence of intramolecular and intermolecular exchange between spin-carrying centers in this kind of supramolecularly ordered multispin systems is favorable for the formation of magnetically interacting chains and two-dimensional networks. © 2016 Wiley Periodicals, Inc.

The Pauli exclusion principle requires that spin orbitals have occupations between zero and one. For pure quantum systems, however, the occupations of the spin orbitals are constrained by additional inequalities known as the generalized Pauli constraints. If the occupation numbers saturate (or nearly saturate) the generalized Pauli constraints, then the occupation numbers are said to be pinned (or quasi-pinned) to the constraints. Here, we assess the complexity of electron correlation of excited states from the pinning or quasi-pinning of the occupation numbers to the generalized Pauli constraints where the degree of pinning encodes information about the structure of the wave function including correlation and entanglement. Results are presented for three- and four-electron atoms and molecules, the five-electron cyclopentadienyl radical, and the seven-electron Fenna-Matthews-Olson complex in green-sulfur bacteria. The data shows that even when the ground-state occupation numbers are pinned, the occupation numbers of excited states manifest pinned, quasi-pinned, and unpinned behavior, reflecting the complexity of electron correlation and entanglement in excited states. © 2016 Wiley Periodicals, Inc.

The intermolecular and intramolecular noncovalent interactions involving π-aromatic compounds have attracted increasing attention over the last decades in chemistry, biology and material sciences. In this review, we discuss contemporary computational studies on the nature and strength of H-π, π-π, and anion-π interactions. We emphasize how modern quantum theoretical approaches ahead of experiment can provide insight into the design of new materials and devices by tuning the π-interactions in cooperative and competitive manners. Usefulness of such approaches towards designing new materials is demonstrated with some examples of molecular recognition/sensing, self-assembly/engineering, receptors, catalysts, supramolecules, graphene, and other two-dimensional (2D) materials/devices. © 2016 Wiley Periodicals, Inc.

Entangled photon pairs generated within integrated devices must often be spatially separated for their subsequent manipulation in quantum circuits. Separation that is both deterministic and universal can in principle be achieved through anti-coalescent two-photon quantum interference. However, such interference-facilitated pair separation (IFPS) has not been extensively studied in the integrated setting, where the strong polarization and wavelength dependencies of integrated couplers -- as opposed to bulk-optics beamsplitters -- can have important implications for performance beyond the identical-photon regime. This paper provides a detailed review of IFPS and examines how these dependencies impact separation fidelity and interference visibility. Focus is given to IFPS mediated by an integrated directional coupler. The analysis applies equally to both on-chip and in-fiber implementations, and can be expanded to other coupler architectures such as multimode interferometers. When coupler dispersion is present, the separation performance can depend on photon bandwidth, spectral entanglement, and the linearity of the dispersion. Under appropriate conditions, reduction in the separation fidelity due to loss of non-classical interference can be perfectly compensated for by classical wavelength demultiplexing effects. This work informs the design as well as the performance assessment of circuits for achieving universal photon pair separation for states with tunable arbitrary properties.

A brief background on the quantum wave-packet propagation method for the study of photodissociation dynamics of polyatomic molecules is summarized as a short tutorial review. The main emphasis is on reasons to use the wave-packet propagation method, followed by a description about basic considerations for practical application of the wave-packet method to polyatomic molecules. The considerations are divided into six steps in the following sequence: (1) prerequisite information for related states, (2) search for critical points, (3) selection of coordinates and kinetic energy operator, (4) potential energy surface, (5) propagation of wave-packet, and (6) analysis of the propagated results. Limitations of the present review and a very brief perspective are given as concluding remarks. © 2016 Wiley Periodicals, Inc.

A facile one-step fabrication of large-area multicolored emissive photopatterns in mixed quantum dot-polymer films is demonstrated. This is in sharp contrast to the current photopatterning approaches that utilize only a single quantum dot (QD) component for single-color patterns. Strategies are presented that allow for either selective or collective modification of specific predetermined photoluminescent peaks of green and red QDs during photopattern development. These strategies yield novel patterns and allow for unprecedented control over how the color contrast of the photopattern evolves with continuous light illumination. These results clearly show that the evolution of the emission spectra of a multicolor mixed QD-polymer film can be readily tailored during pattern development, either by careful selection of the excitation wavelength or through combinations of controllably unstable and stable QDs with different recovery rates. Notably, these strategies are simple, fast, and robust, yielding high-resolution microscopic patterns over large areas (up to fractions of a cm2). Furthermore, the flexibility and capabilities of these strategies greatly expand the potential applications of multicolor emissive photopatterns, particularly in the areas of sensing, imaging, and lasing systems where it is important to exert delicate control over the intensity of selected colors within specific spatial regions.