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The carbon trimer, $ \hbox {C}_3 $ C 3 also known as propadienediylidene, is a quasi-linear molecule with an unusual electronic structure and a very flat bending potential in its ground electronic state. $ \hbox {C}_3 $ C 3 is an important species in astrophysics and carbon plasmas. Observed transition wavenumbers within and between the $ \tilde {X}\,^1\Sigma ^+_{\rm g} $ X ~ 1 Σ g + and $ \tilde {A}\,^1\Pi _{\rm u} $ A ~ 1 Π u states of $ \hbox {C}_3 $ C 3 are extracted from 21 papers and then subjected to a Measured Active Rotational-Vibrational Energy Levels (MARVEL) analysis: a corrected list of 4940 transitions are inverted to yield 1887 empirical energy levels. Uncertainties for these levels are determined using a newly implemented bootstrap method. These levels will provide input for developing a full spectroscopic model for $ \hbox {C}_3 $ C 3 which can used to generate a line list for the $ \tilde {X}\,^1\Sigma ^+_{\rm g} $ X ~ 1 Σ g + and $ \tilde {A}\,^1\Pi _{\rm u} $ A ~ 1 Π u states. [ABSTRACT FROM AUTHOR]

The carbon trimer, $ \hbox {C}_3 $ C 3 also known as propadienediylidene, is a quasi-linear molecule with an unusual electronic structure and a very flat bending potential in its ground electronic state. $ \hbox {C}_3 $ C 3 is an important species in astrophysics and carbon plasmas. Observed transition wavenumbers within and between the $ \tilde {X}\,^1\Sigma ^+_{\rm g} $ X ~ 1 Σ g + and $ \tilde {A}\,^1\Pi _{\rm u} $ A ~ 1 Π u states of $ \hbox {C}_3 $ C 3 are extracted from 21 papers and then subjected to a Measured Active Rotational-Vibrational Energy Levels (MARVEL) analysis: a corrected list of 4940 transitions are inverted to yield 1887 empirical energy levels. Uncertainties for these levels are determined using a newly implemented bootstrap method. These levels will provide input for developing a full spectroscopic model for $ \hbox {C}_3 $ C 3 which can used to generate a line list for the $ \tilde {X}\,^1\Sigma ^+_{\rm g} $ X ~ 1 Σ g + and $ \tilde {A}\,^1\Pi _{\rm u} $ A ~ 1 Π u states. [ABSTRACT FROM AUTHOR]

By using genetic algorithm combined with B3LYP and QCISD methods, this paper investigates the stabilities and electronic structures of Al6OMm (M = Na, K; m = 2,4,6) and a few other AlnXNam (X = C, N, O) clusters. The results show that the nonmetal doped metal clusters with 26 valence electrons have enhanced stabilities and large energy gaps. This paper extends the Jellium model for the application to the nonmetal doped metal clusters and explains the electronic origin of this strong magic structure. The nonmetal X atom is situated in the centre of the magic clusters. The 2s/2p orbitals of the central atom interact strongly with the superatomic 1S/1P orbitals and form bonding and antibonding orbitals. The bonding orbitals make the C/N/O atoms form s2p6 shell closure, and the antibonding orbitals make the metal moieties form closed 2S22P6 shells. The 26 valence electrons form closed s2p6S2P6D10 shells, and this electronic configuration can be taken as the combination of the octet rule and 18-electron rule. The octahedral Al6O2− core is a superatomic anion with great stability, and it can be used as building blocks to assemble Zintl phase materials by interaction with alkali metals. [ABSTRACT FROM AUTHOR]

Photochemical reactions often involve states that are closely coupled due to near degeneracies, for example by proximity to conical intersections. Therefore, a multistate method is used to accurately describe these states; for example, ordinary perturbation theory is replaced by quasidegenerate perturbation theory. Multiconfiguration pair-density functional theory (MC-PDFT) provides an efficient way to approximate the full dynamical correlation energy of strongly correlated systems, and we recently proposed compressed multistate pair-density functional theory (CMS-PDFT) to treat closely coupled states. In the present paper, we report the implementation of analytic gradients for CMS-PDFT in both OpenMolcas and PySCF, and we illustrate the use of these gradients by applying the method to the excited states of formaldehyde and phenol. [ABSTRACT FROM AUTHOR]

In this paper, we have conducted a systematic research on the single- and double-sided adsorption models of Al atoms on the surface of graphene. The results show that the adsorption energy of single-sided Al atoms on each active site on perfect graphene is about − 1.0 eV . When a single C vacancy exists, the adsorption energy of Al atom on the surface of single-vacancy graphene is − 5.42 eV , and when two C vacancies exist, the adsorption energy of Al atom on the surface of double-vacancy graphene is − 2.76 eV . Subsequently, the adsorption behaviour of Al atoms on both sides of graphene was systematically studied. The calculation results showed that the adsorption energy of Al atoms on both sides of perfect graphene was twice that of Al atoms on one side of perfect graphene. At the same time, when Al atoms are adsorbed on both sides of graphene with vacancies, the adsorption performance is improved from − 2.25 eV to − 4.84 eV . In conclusion, the existence of vacancies is of great significance for the adsorption performance of Al atoms on the graphene surface. Our research results provide a theoretical basis for the further development of graphene-metal matrix composites. [ABSTRACT FROM AUTHOR]

Novel ways to reduce the computational effort for atomic structure prediction while retaining high accuracy are of wide interest. This paper describes an implementation of the method of averaging over the wave vector k for the description of the lithium condensation. We show that the direct transition from the gas phase to the crystalline one is complicated. The formation of the crystal structure occurs through the condensation of individual small clusters. [ABSTRACT FROM AUTHOR]

The good performance of a photovoltaic device requires fitting a series of parameters related to electronic structure of materials. Since it is well-known that fullerenol is an excellent electron acceptor with excellent electron conductivity, in this paper we analyse the electronic levels, energy gaps, absorption spectra and electron mobility of hydroxylated La@C 82 (La@C 82 (OH) n , n = 0−32) endohedral metallofullerene. Furthermore, calculations was performed on one unit of three donor polymers with low energy of the lowest unoccupied molecular orbital and on the well-known acceptor fullerene derivative [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) in order to compare the electronic structure and possible donor–acceptor combinations. Interestingly, high coatings have larger energy gap between the highest occupied molecular orbital of donor and the lowest unoccupied molecular orbital of acceptor, which is essential for increasing the open circuit voltage, which relates directly to power conversion efficiency. On the other hand, low coatings have better electron mobility, which is essential in electron transport layers in perovskite-based solar cells. Finally, the absorption spectra of fullerenols were also calculated and compared with the widely used in organic solar cells PC 61 BM, obtaining a broader absorption spectrum in hydroxylated endohedral metallofullerenes helping in the performance of fullerenols for harvesting the solar spectrum. [ABSTRACT FROM AUTHOR]

The effects of bend angle on the stability, electronic structure and optical properties of Li-absorbed borophene system are studied by using density functional theory based on the first principles. The structure of borophene did not change significantly after adsorption of a Li atom, and the planar structure of borophene was not destroyed. Bending deformation affects the stability of the adsorption system and reduces the binding energy of the adsorption system. The adsorption of Li atoms obviously changes the energy band structure of borophene, and more impurity levels appear in the conduction band. The 2s orbital of Li and the 3p orbital of B are obviously hybridised. A charge transfer occurs between Li atoms and borophene. As the deformation increases, the amount of charge transfer increases. The bending angle affects the size of the absorption peak and reflection peak of the adsorption system. [ABSTRACT FROM AUTHOR]

Boron nitride nanotubes (BNNTs) are semiconductors with a wide band gap. In comparison with carbon nanotubes (CNTs), BNNTs have higher chemical stability, excellent mechanical properties and higher thermal conductivity. In this paper, we study the effect of diameters and substituting B and N atoms of various zigzag BNNTs with Al, on structural and electronic properties of BNNTs in solid state using the density functional theory method. The results of calculations of density of states and band structure (band) showed that the band gap between the valence and conduction level increases as a result of the enhancement of tube diameter of BNNTs. Finally, the results showed that the electronic properties of the pristine BNNTs can be improved by doping Al atom in the zigzag configuration of tubes. [ABSTRACT FROM AUTHOR]

Can a C60layer cover a surface of single-wall carbon nanotube (SWCNT) forming an exohedral pure-carbon hybrid with only van der Waals interactions? The aim of the present paper is to address this question and to demonstrate that the fullerene shell layer in such a bucky-corn structure can be stable. Theoretical study of the structure, stability and electronic properties of bucky-corn hybrids is reported for the shell of C60and C70molecules on an individual SWCNT, C60dimers on an individual SWCNT as well as C60molecules on SWNT bundles. The geometry and total energies of the bucky-corn hybrids were calculated by the molecular dynamics method, while the density functional theory method was used to simulate the electronic band structures. [ABSTRACT FROM AUTHOR]

The electronic structure and spectroscopy of some representative dinuclear compounds containing CpM(CO)3 and CpM(CO)2 groups were studied using TDDFT (Time Dependent Density Functional Theory). These compounds contain Cp (cyclopentadienyl) as a ligand, and M can be Cr, Mo or W. Their main electronic transitions were calculated and the results are in good agreement with the experimental data. This allows the assignment of some bands whose origin was not clear. In all the cases, the carbonyls and Cp groups restrict the symmetry. The molecular orbitals that would be involved in M-M bonding interact strongly with the carbonyls and show unusual shapes and occupations. The strongest electronic bands are caused by σ→σ* transitions in most of the molecules containing CpM(CO)3 groups, whereas in molecules such as Cp(CO)2M≡M(CO)2Cp the most intense bands are produced by π→π* transitions. The origin of other bands is now explained. The effect of the solvent on the electronic transitions and the use of EOM-CCSD method in some compounds were also checked. [ABSTRACT FROM AUTHOR]

The low-lying electronic states of silicon dimer (Si 2 ) and its cation (Si 2 + ) have been studied by single-photon photoelectron spectroscopy combining a flow-tube reactor, vacuum-ultraviolet synchrotron radiation, and a double imaging photoelectron/photoion spectrometer. The energy range covered in this study (7.0−9.5 eV) allowed to observe several photoionising transitions involving the three lowest electronic states of Si 2 ( X 3 Σ g − , D 3 Π u , a 1 Δ g ) and five of the six lowest states of Si 2 + ( X + 4 Σ g − , a + 2 Π u , b + 2 Δ g , c + 2 Σ g − , and e + 2 Π u ). Using ab initio calculations and Franck-Condon simulations, several electronic transitions are identified which bring new elements in the description of the dense electronic landscapes of the silicon dimer and its cation. Interestingly, one of the most intense transitions is spin-forbidden ( X + 4 Σ g − ← a 1 Δ g ) and is most probably observed through autoionisation processes by spin interactions. [ABSTRACT FROM AUTHOR]

As part of a computational study of the thermochemical properties of systems related to carbonic acid (H 2 CO 3 ), an interesting phenomenon was observed in the bicarbonate radical (HCO 3 ). This species belongs to the class of formoxyl radicals, but lacks the C 2 v geometric symmetry of the more heavily-studied and prototypical HCO 2 and FCO 2 molecules. However, it is not immune from the problems that those molecules present to electronic structure calculations. Specifically, at geometries in the vicinity of the equilibrium structure, three solutions to the unrestricted Hartree-Fock equations can be found: two in which the unpaired spin is largely localized onto one of the (inequivalent) carbonyl oxygen atoms, and one in which the spin is delocalized. While all three of these reference functions comprise orbitals that transform as pure irreducible representations of the C s point group, the two localized choices qualitatively correspond to the symmetry-broken solution of the C 2 v formoxyl species and the delocalized solution qualitatively corresponds to the symmetry-preserving (but orbitally unstable) solution. The three solutions are described in this work, as well as the corresponding ambiguities that result in the thermochemical characterization of this species. [ABSTRACT FROM AUTHOR]

The electronic structure of molecules is routinely examined for static arrangements of point nuclei, which is a highly useful premise but not without certain limitations. Here, the electron-nuclear correlation energy is analysed in the context of the quantised nuclear energy associated with the chemical bond vibrations. To this end, accurate calculations of the ground state of a hydrogen atom (including basis functions in the energy continuum) whose nucleus is confined by a quadratic potential well, are performed for all values of the spring constant. The numerically exact ground state energy is compared to the results obtained within the Born–Oppenheimer approximation and within the uncorrelated product wavefunction ansatz. The electron-nuclear correlation energy is found to be smaller in magnitude than the electron correlation in two-electron atomic systems, in the limit of weak nuclear confinement, and is further reduced by at least an order of magnitude in the limit of strong confinement. In all cases, however, the electron-nuclear correlation energy is found to be significantly larger than the error of the Born–Oppenheimer approximation. Moreover, the error of the Born–Oppenheimer approximation is found to persist within the limit of infinite nuclear confinement. Insight into the electron-nuclear correlation energy from this study will help incorporate the nuclear quantum effects into the electronic structure theories. [ABSTRACT FROM AUTHOR]

In this Article, we extend our XANESNET deep neural network (DNN) to predict the lineshape of first-row transition metal K-edge valence-to-core X-ray emission (VtC-XES) spectra. We demonstrate that – despite the strong sensitivity of VtC-XES to the electronic structure of the system under study – the DNN can reproduce the main spectral features from only the local coordination geometry of the transition metal complexes when encoded as a feature vector of weighted atom-centred symmetry functions (wACSF). We subsequently implement and evaluate three methods for assessing uncertainty in the predictions made by the VtC-DNN: deep ensembles, Monte-Carlo dropout, and bootstrap resampling. We show that bootstrap resampling provides the best performance when evaluated on 'held-out' testing data, and also demonstrates a strong correlation between the uncertainty it predicts and the error occurring between the target and predicted VtC-XES spectra. Finally, we demonstrate practical performance by application to unseen transition metal complexes across the entire first-row (Ti–Zn). [ABSTRACT FROM AUTHOR]

The approximate CNDOL Fockian, together with the configuration interaction of single excitations ([CIS|CNDOL/21]), is applied to investigate the electronic properties of three different kinds of donors (D) considered suitable for photovoltaic devices, either as isolated systems or complexed with fullerene (C60) as potential acceptors (A). Calculated charge maps, together with the Coulomb-exchange term of CIS lowest transitions, are used to understand the electronic topology and possible behaviour of D-A excitons. The effects of varying donor structures are compared. The lowest excitation energies of the donor-C60 complexes arise from electron densities localised at the central ring units in the donors. Nevertheless, C60 does not always participate in electron sharing upon excitation. It sometimes acts only as a structural companion for enhancing or not the exciton capability to provide adequate photoelectric power conversion efficiencies. The [CIS|CNDOL/21] method is validated as a valuable tool for modelling structure-related properties of molecular excitons and for predicting the performance of D–A materials in relatively big supramolecular systems. It is shown that multi-electron CIS wavefunctions are at least as useful as one-electron molecular orbitals to describe charge-transfer properties of excitons and provide a physical picture of the whole electron density. [ABSTRACT FROM AUTHOR]

The Zinc telluride (ZnTe) system presents appealing optoelectronic properties used in radiology as well as in the detection of terahertz radiation (THz). In this work, we report a theoretical investigation of the ground and excited states of ZnTe and its ions ZnTe+ and ZnTe- using different ab inito methods. The potential energy curves (PEC) are computed using the CASSCF/LANL2DZ and MRCI/LANL2DZ methods. These curves allow inferring the different spectroscopic constants such as the internuclear distance (Re), the harmonic vibration frequency (ωe), the rotation constant (Be) and the dissociation energy (De). Our results indicate that the electronic states of ZnTe and its ions converge to several lower dissociation limits. The existence of unstable and crossings states is due to the presence of rotational and spin–orbit interactions. The results obtained are compared to the existing experimental data and have generally shown a reasonable agreement. [ABSTRACT FROM AUTHOR]

We investigate the local polarisability or polarisability density using both a conceptual density functional theory approach based on the linear response function and time-dependent density functional theory. Using a zero frequency in the latter, we can immediately compare both approaches. Using an analytical expression for the linear response kernel, we are able to systematically analyse α(r) throughout the periodic table. An extension to molecules is also made with a study of the CO molecule retrieving the connection between local softness and local polarisability. [ABSTRACT FROM PUBLISHER]

The adsorption properties of BC3 nanosheets on radioactive metal atoms were systematically investigated based on the first principles approach of density functional theory (DFT). Following the adsorption of metal atoms by BC3, an electronic structure analysis was performed to determine the optimal adsorption sites and energies of metal atoms. The impact of temperature on the adsorption rate was calculated using the adsorption energy obtained from the first-nature principle. BC3 is more stable than graphene material, with less impact on adsorption rate at high temperatures, and forms chemical bonds with radionuclides, significantly enhancing adsorption performance (especially on Ag, transforming it from physical to chemisorption). The results indicate that the B-atom-doped graphene materials have a promising future for the post-treatment of radioactive effluents in nuclear wastewater. [ABSTRACT FROM AUTHOR]

Transition metal-doped boron clusters have attracted much attention due to the novelty of electronic properties and structural evolution in recent years. In this work, we use the efficient CALYPSO structure search method to perform the globally minimum structure search for the neutral and negative Ta2Bn(n = 1–10) clusters. Then DFT optimisation was carried out at the pbe1pbe level to obtain a lot of low-energy stable structures. Finally, the total energy was sorted to select the ground-state and low energy structure. The results show that the cluster forms a B ring when n = 6. With the number of B atoms increases, the B ring with the line of two Ta atoms as the axis becomes larger and larger. Neutral Ta2B6 clusters with bipyramid structure and protruding stability were found by relative stability analysis, the HOMO–LUMO gap was 2.75 eV. The chemical bonds of closed-shell D6h Ta2B6 were analysed by using the adaptive natural density partitioning (AdNDP) method. It was found that the interaction between the B6 ring and the apex Ta atom is carried out by six 4c-2e π bonds. In addition, bonding analysis shows that the strong d-p interaction between tantalum and boron atomic orbitals can effectively improve the stability of Ta2B6 clusters. [ABSTRACT FROM AUTHOR]

The electronic structure and optical properties of the black phosphorene adsorbed O-atom system were studied by the method based on the first principle of density generalised theory with different coverage and bending angles. The black phosphorene adsorbed O-atom system is the most stable when the coverage is 5.56%. When the coverage is 8.33%, the bandgap reaches a maximum and changes from direct to indirect bandgap. The total density of states is contributed by both P and O atoms, with O atoms making the main contribution to the valence band part. With the increase of coverage, the black phosphorene adsorption O-atom system shows a blue shift at the reflection peak. With the increase of the bending angle, the adsorption energy gradually decreases and the stability of the structure decreases. The bandgap reaches the maximum at a bending angle of 50, and the absorption coefficient and reflectance at the absorption and reflection peaks are the smallest, and the absorption and reflection of light are the first to stop. When the bending angle is larger than 50, it can make the system change from indirect bandgap to direct bandgap, and it is easy to realise the stable regulation of bandgap. [ABSTRACT FROM AUTHOR]

The effects of different doping concentrations and hydrogenation on the electronic structure and optical properties of Al-doped germanene were studied based on a density generalised theory first-principles approach. It was found that the system with a doping concentration of 3.125% was more stable. The bandgap is lower than 0.1 eV for doping concentrations of 3.125% to 6.25%, which is consistent with the nature of semimetals. The bandgap transition from indirect-direct-indirect is achieved at doping concentrations of 11.11% to 25%. Both the s- and p-states of Al and Ge atoms contribute to the total density of states compared to the intrinsic germanene, and the doping of Al promotes the absorption and reflection of light from germanene and also undergoes different degrees of blue shift. Hydrogenation has a large effect on the electronic structure of Al-doped germanene, making the s and p state's electronic interactions of Al atoms weaker. The Al-doped germanene system can be converted from indirect bandgap to direct bandgap when fully hydrogenated. [ABSTRACT FROM AUTHOR]

The internal connection between the electronic structure and decomposition mechanism for ANTA and AHNTA is investigated by DFT method. The molecular electrostatic potential shows that hydrogen atoms of the amino group are easily transferred to the nitro group. The excitation process of S0→T1 can be regarded as the local π → π ∗ excitation. For the substituent dissociation, amino group is easily separated from the ring. For the ring cleavage, the C–N bond will be weakened by substituents on the C and N atoms. Especially at the excited state, the C–N bond with a nitro group on the C atom is the easiest to break. The charged state is beneficial to CONO isomerisation, and the H transfer is promoted at the excited state. For ANTA, the reaction rate of CONO isomerisation is faster than ring cleavage at the ground or the positively charged state. At the negatively charged state, the reaction rate of H transfer is the fastest. For AHNTA, at the ground state or the charged state, the reaction rate of CONO isomerisation is the fastest, compared to ones of the H transfer and ring cleavage reactions. At the excited state, the order is k(H transfer)>k(ring cleavage) for ANTA and AHNTA. [ABSTRACT FROM AUTHOR]

The 2 Π g ← X 2 Σ u + electronic spectrum of C 5 + in the gas-phase with origin band at 513 nm is reported following experiments in a cryogenic ion trapping instrument. Buffer gas-cooled C 5 + ions, generated by laser vaporisation of graphite, were investigated using two action spectroscopy approaches. Laser-induced dissociation of weakly bound C 5 + − He n complexes synthesised in the trap reveal a linear dependence of the absorption energies on n allowing prediction of those of the bare ion C 5 + . These results are confirmed in two colour experiments on C 5 + , by monitoring fragmentation into the C 3 + + C 2 product channel. The data are supplemented with high-level electronic structure calculations which support the assignment of D ∞ h symmetry to the ground electronic state. These laboratory results provide the requisite data needed for spectroscopic detection of this structure in terrestrial and extraterrestrial environments. [ABSTRACT FROM AUTHOR]

By means of first-principles calculations, we investigate the effect of Cr, Mn impurities on the magnetic and optical properties of 4H-SiC. We find the Cr atom monodoped 4H-SiC has the more stable configuration. The Cr monodoped, Co monodoped, (Cr, Co) co-doped and (Cr, Co, VSi) co-doped 4H-SiC system all can induce magnetism. The results indicate that (Cr, Co) co-doped 4H-SiC has the strongest ferromagnetism with ΔE of −489.7 meV. The magnetic coupling between the magnetic moments and the strong ferromagnetic coupling caused by Cr and Mn doping can be attributed to the p-d hybrid interaction. The silicon vacancy has a negative influence on the local magnetic moments of Mn atom of (Cr, Mn) co-doped 4H-SiC. When transition metals (TM = Cr, Mn atoms) are introduced into 4H-SiC, the imaginary part of the dielectric function and the adsorption spectrum are both red-shifted with the change of band gap. The results provide a new route for the potential applications of dilute magnetic semiconductors in spintronic devices by transition metal (TM = Cr, Mn atoms) doped 4H-SiC. [ABSTRACT FROM AUTHOR]

On the basis of the time-dependent density functional theory (TD-DFT) method, two C 28 isomers and three C 30 isomers were theoretically distinguished by C 1s X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy of the carbon K-edges. The NEXAFS spectra exhibit a strong dependence on the symmetries of the five different kinds of isomers in comparison to XPS. So it can be well employed to identify the two kinds of C 28 isomers and three kinds of C 30 isomers by NEXAFS spectra. Besides, the spectra, which are generated by carbon atoms with different chemical environments in fullerene are also studied, so as to determine the source of each characteristic peak in the total spectra. [ABSTRACT FROM AUTHOR]

In this contribution, we investigate the nature of the electronic interaction between gas phase CO and NO with coinage metal atoms {Cu, Ag, Au} in different charge states. The electronic structure is first characterised by means of state-of-the-art coupled-cluster calculations for a wide range of configurations. An analytical Reactive Bond Order (REBO) force field is used to fit the data, revealing a strong corrugation of the potential energy landscape in some cases. The fundamental vibrational bands are variationally computed for the different system. It is found that the metal determines the binding interaction and the spectroscopic signature of the complexes, as well as their structure and geometry. [ABSTRACT FROM AUTHOR]

We make an initial exploration of a spectral filtering approach to numerically approximating solutions to the time-independent Schrödinger equation for a model system of two spinless fermions with harmonic interactions. Fourier transformation of the time evolution of an arbitrary antisymmetrized wave packet results in resonance at frequencies proportional to eigenenergies of the system Hamiltonian, while the Fourier coefficient approximates the corresponding eigenfunction. Spectral filtering is explored using the two-particle model through both direct numerical integration of the Schrödinger equation and a semiclassical parametrisation. In the former, a discrete position basis describes the time-evolution operator, which is then repeatedly applied to an antisymmetrized wave packet to obtain the packet's time evolution. In the semiclassical parametrisation, equations of motion for the parameters are obtained from the Dirac-Frenkel-McLachlan functional. Integration of the parameter equations of motion describes the packet's time evolution. The semiclassical approach requires less memory and accurately obtains the eigenspectrum. In a step towards application of spectral filtering to realistic systems, a possible ansatz for use with Coulomb potentials is explored, using a simple model Hamiltonian. [ABSTRACT FROM AUTHOR]

The ultraviolet photodissociation of the prototypical organometallic half-sandwich compound dicarbonylcyclopentadienyliodoiron(II) [η5-CpFe(CO)2I] has been studied in the gas phase across the wavelength range 260 ≤ λ ≤ 310 nm using multi-mass velocity-map ion imaging with photoproducts detected using both resonance enhanced multiphoton and vacuum ultraviolet (λ = 118.2 nm) single photon ionisation methods. Ion images recorded for the atomic iodine and the cyclopentadienyl photoproducts reveal fast, anisotropic components to their recoil velocity distributions. The experimental work is supported by multi-reference (spin–orbit averaged) electronic structure calculations that suffice to illustrate the high electronic state density in such transition metal complexes and provide insights into the rival fragmentation dynamics. The ground state parent molecule has singlet spin multiplicity, but the product energy disposal measured following Fe–Cp bond fission shows the involvement of nominally spin-forbidden transitions. The Fe–I and Fe–Cp bond fissions should both be viewed as homolytic and occurring on excited state potentials that are dissociative in the relevant ligand elimination coordinate. [ABSTRACT FROM AUTHOR]

A new carbon allotrope orthorhombic oC240, is proposed by first principles calculation. The unit cell of oC240 is composed of 240 carbon atoms. The calculated elastic constants and phonon spectra confirmed that oC240 is mechanically and dynamically stable under ambient pressure. The calculated hardness is 56.3 GPa. The electronic structure calculations show that oC240 is an indirect band gap semiconductor with the gap of 2.13 eV. [ABSTRACT FROM AUTHOR]

Fundamental principles for theoretical understanding and elucidation of structure and reactivity of iron-sulfur (Fe-S) FenSm (n, m=2∼8) clusters are investigated and elucidated on the theoretical and experimental grounds. To this end, the nature of chemical bonds of these clusters is investigated by three methods; (1) the spin Hamiltonian model for analysis of EPR results, (2) broken-symmetry (BS) hybrid density functional theory (HDFT) methods for full geometry optimisations and elucidations of complete active spaces (CAS) for one-electron transfers reactions and (3) beyond HDFT methods such as CAS configuration interaction (CI) and MR CI for high precision energy calculations on classical and quantum computers. Theoretical concepts revealed are applied for elucidation of the mechanism of nitrogen fixation with FeMoco (Fe7MoS9C) cluster, indicating an important role of proton-coupled (PC) one electron spin transfer (OEST) processes instead of radical reaction mechanisms. [ABSTRACT FROM AUTHOR]

The geometries, stabilities and electronic structures of AlnCum (n = 5–9, m = 1–3) clusters were explored by using the genetic algorithm combined with ab initio methods. The geometric structures are almost spherical when the valence electrons are around the magic number 20, otherwise the structures are oblate or prolate. The stabilities of the clusters are related to both the Cu/Al ratios and the electronic configurations. The clusters with lower Cu/Al ratios have high stabilities. The molecular orbitals are in accord with the shell structures predicted by the jellium model. The 3d orbitals of the Cu atoms are localised, although their orbital energies are between the 1P and 1D jellium orbitals. The Al6Cu2 with 20 valence electrons forms closed 1S21P61D102S2 shells, and shows large binding energy and removal energy, large ionisation potential and small electron affinity. For the no-magic clusters, the structure deformation leads to crystal-field-like splitting of the degenerate shells and stabilises the clusters. [ABSTRACT FROM AUTHOR]

A series of blue phosphorescent heteroleptic cyclometalated Ir(III) complexes with mesitylphenyl-imidazole ligands for organic light-emitting devices have been theoretically studied. We want to find their electronic structures, spectroscopic properties, and application value for organic light-emitting devices. (fppz)2Ir(acac), (fppz)2Ir(tpip), (dfbdp)2Ir(fppz), (F-fppz)2Ir(acac), (F-fppz)2Ir(tpip), and (dfbdp)2Ir(F-fppz) are investigated with DFT and TD-DFT approaches, where, for (fppz)2Ir(acac), (fppz denotes 2-(5-(trifluoromethyl)-4H-pyrazol-3-yl)pyridine, and acac denotes acetylacetonate); for (fppz)2Ir(tpip), tpip denotes tetraphenylimido-diphosphinate; and, for (F-fppz)2Ir(acac) and (F-fppz)2Ir(tpip), F-fppz denotes 2-(5-fluoro-4H-pyrazol-3-yl)pyridine. [ABSTRACT FROM AUTHOR]

The electronic structures of C/B/Al-doped armchair GaN nanoribbons (aGaNNRs) are systematically studied by using density functional theory. We find that the original aGaNNRs are direct band gap semiconductors and that the gaps monotonically decrease with increasing widths. Interestingly, the B- or Al-doped aGaNNRs are also direct-band gap semiconductors with a slightly larger gap than their undoped aGaNNRs, while the C-doped aGaNNRs display metallic characteristics with an impurity state across the Fermi level in band structures. The semiconducting or metallic behaviours of C/B/Al-doped aGaNNRs can be explained by the orbital coupling between the extrinsic atom and primary Ga, N in their partial density of states. Our results show a useful way to modulate the band gaps of aGaNNRs. Using the density-functional theory, we performed a theoretical research to study the electronic structures of C/B/Al-doped armchair gallium nitride nanoribbons. The calculated band structures show that the perfect and original aGaNNRs are direct semiconductors regardless of ribbon widths, and gaps monotonically decrease with increasing the widths. The B/Al-doped aGaNNRs are semiconductors with a slightly larger gap, while metallic behavior presents in C-doped aGaNNRs with an impurity band across the EF. The results show a useful way to modulate the band gaps of aGaNNRs. [ABSTRACT FROM AUTHOR]

The atomic substitutions were used to study the hole transport materials (HTM) properties of six thiophenothiophene molecules (HTM1-HTM6) to reveal the relationship between their core structures and photoelectric properties. To better investigate the difference between experimentally original and designed molecules, we calculated the hole mobility and some parameters (such as energy levels, stability, and optical properties, etc). The results showed that the molecular orbital levels of the original and designed molecules have well matched with perovskite and Ag electrode to ensure hole transport and inhibit the electron reflux. Among the designed HTMs, HTM5 has the smallest energy gap that results in the red-shifted absorption spectra. Furthermore, there is an obviously increased charge transfer integral V due to the introduction of the Si atom, which greatly improved the hole mobility. Therefore, atom substitution by introducing Si atoms (HTM5) will improve the energy levels and charge transport ability, and molecular design by means of atom substitution can be a potential way to tunable HTM performance in solar cells. [ABSTRACT FROM AUTHOR]

Three-center nuclear attraction integrals, which arise in density functional and ab initio calculations, are one of the most time-consuming computations involved in molecular electronic structure calculations. Even for relatively small systems, millions of these laborious calculations need to be executed. Highly efficient and accurate methods for evaluating molecular integrals are therefore all the more vital in order to perform the calculations necessary for large systems. When using a basis set of B functions, an analytical expression for the three-center nuclear attraction integrals can be derived via the Fourier transform method. However, due to the presence of the highly oscillatory semi-infinite spherical Bessel integral, the analytical expression still remains problematic. By applying the S transformation, the spherical Bessel integral can be converted into a much more favorable sine integral. In the present work, we then apply two types of double exponential transformations to the resulting sine integral, which leads to a highly efficient and accurate quadrature formula. This method facilitates the approximation of the molecular integrals to a high predetermined accuracy, while still keeping the calculation times low. The fast convergence properties analyzed in the numerical section illustrate the advantages of the method. [ABSTRACT FROM AUTHOR]

Density functional theory calculations have been carried out on ternary PtmAunAgl clusters of low nuclearity (m + n+l = 5, 6 and 7). Various properties including average bond distance, binding energy, mixing energy, ionisation potential, electron affinity, HOMO–LUMO gap and fragmental channel, are reported for the optimised structures. The variations of the calculated properties of the PtmAunAgl clusters as a function of concentrations (i.e. all m-, n-, and l-values) are displayed by ternary diagrams. The geometric, energetic and electronic properties are sensitive to the composition and size of PtmAunAgl clusters. [ABSTRACT FROM AUTHOR]

In this manuscript, the electronic structure, bonding nature and optical properties of the ternary Ba2HgS5 compound was investigated using the density functional theory (DFT). The generalised gradient approximation (GGA), Engel and Vosko generalised gradient approximation (EV-GGA) and the modified Becke Johnson (mBJ) schemes were used to model the exchange and correlation potentials. Band structure calculations indicate that this compound has a direct energy band gap value of 2.34 eV, showing a close agreement with the experimental band gap value of 2.40 eV. The energy band gap value calculated using the mBJ formalism is larger than those obtained from the GGA and the EV-GGA approaches. From the analysis of the partial electronic energy density of states, it was observed that the valence band is dominated by the Ba-p, S-s and Hg-d electronic states, while the conduction band is formed by the S-p and Ba-d orbitals. In addition, there exists a strong hybridisation in the valance band and in the conduction band between the S-p and Hg-s, Ba-s and Hg-f, Hg-s, S-p as well as the S-p and Hg-p states, respectively. This strong hybridisation leads to strong covalent bonding between the Hg-S and Ba-S atoms. Moreover, the optical constants were calculated and discussed in details. The energy dependent optical parameters were found to be anisotropic with respect to the polarisation of the incident electromagnetic wave and exhibit features in complete agreement with the electronic band structure calculations. The compound absorbs ultraviolet radiation quite strongly. Ba2HgS5 possesses high refractive index over a wide range of frequency and has potential to be used as anti-reflective coating and also in photonic devices like in light emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

Electronic structure calculations are carried out for the S4 molecule at the CCSD(T)-F12a/VTZ-F12 level of theory to map out its potential energy surface, which possesses a double-well shape with a low-energy barrier. Two degrees of freedom are considered: the distance R and the gearing motion angle between the two weakly-perturbed S2 dimers, which form S4. Vibrational states are computed on this 2D-surface and assigned quantum numbers based on their energies and the shapes of their wave functions. Two progressions of vibrational states are identified: a long progression of easily assignable states that develop nodes along the 'channels' on the surface, and a shorter progression of states that develop nodes across the 'channels' and are much harder to assign, due to the double-well effect. Normal mode analysis indicates that these two modes in S4 represent a significant mixture of conventional bending and stretching motions. When the angle is increased, the lower frequency mode corresponds to stretching of the distance R, while the higher frequency mode corresponds to compression of R. Frequencies of the modes, ∼180 and ∼420 cm−1, are in a qualitative agreement with earlier ab initio studies of tetra-sulfur, and with sparse experimental data. [ABSTRACT FROM AUTHOR]

The All Configuration Mean Energy (ACME) conditions are a special case of state averaging for Multiconfigurational Self-Consistent-Field (MCSCF) orbital optimisation. The method is formulated using the Graphical Unitary Group Approach (GUGA) in which the Configuration State Function (CSF) basis is represented as walks within a Shavitt graph. This graphical formulation leads to efficient recursive algorithms for the energy and reduced density matrices (RDM) that are independent of the CSF dimension and that scale only as O(n2) where n is the number of occupied orbitals. The Hamiltonian matrix diagonalization step is obviated and the CSF expansion coefficients are neither referenced nor required during the orbital optimisation. This allows MCSCF orbital optimisation to be performed for essentially unlimited numbers of active orbitals and arbitrarily large CSF expansions. The discussion includes various types of CSF expansion spaces, the partitioning of the essential and redundant orbital optimisation parameters, the computation of the spin-density, and the formulation of state-specific analytic gradients and nonadiabatic coupling for high-level electronic structure methods that use the ACME MCSCF orbitals. [ABSTRACT FROM AUTHOR]

The structures and the vibrational dynamics of the complexes HHe are investigated experimentally (via mass spectrometry (MS)) and at high levels of electronic-structure theory. The MS measurements reveal interesting trends about the stability of the starting members of the HHe family. The computations establish that the basically linear, strongly bound, symmetric triatomic molecular ion He(H)He, with an equilibrium H–He distance of 0.925 Å and about 2/3 but at least 1/2 of the positive charge on H, is the molecular core of all of the complexes. Definitive quantum-chemical results are obtained for HHe and HHe , including the proton affinity of He (computed to be cm−1 via the focal-point analysis (FPA) scheme), the FPA isomerisation energy between the two linear isomers of HHe (cm−1), and the dissociation energy of the HHe HHe + He reaction, with an FPA estimate of cm−1. The structural isomers of the He-solvated complexes are discussed up to n=18. A useful notation, [k−l−m]-HHe , is introduced to characterise qualitatively the three possible belts around the He–H –He core in HHe (), where l denotes the number of He atoms in the central belt and denote the number of He atoms in the top and bottom belts. Capping He atoms attached to the belts can be indicated by sub- and superscripts. Several possible indicators of microscopic superfluidity are investigated: He evaporation energies, rotational constants, and vibrational fundamentals. [ABSTRACT FROM AUTHOR]

In a manner similar to but distinct from concurrent tensor efforts in electronic structure, it is shown that the Laplace transform can serve as a generator for a sum-of-products (SOP) form that allows one to write essentially any function of distance between two particles (i.e. any central force potential) as an exact two-body matrix. In particular, exact expressions for the Coulomb, Yukawa and long-range Ewald two-body operators are evaluated in a band-limited (Sinc function) basis. The resultant exact, full-basis, SOP representations for these interaction potentials – acting in conjunction with an external harmonic confining field – are validated via comparison with energy eigenstate solutions obtained via an independent calculation based on separation of variables. The new two-body matrix representations may have substantial impact in any of the many disciplines in which pair-wise central force interactions are relevant – especially, electronic structure and dynamics. [ABSTRACT FROM AUTHOR]

The near-edge X-ray absorption fine structure (NEXAFS) spectra and the X-ray photoelectron spectroscopy (XPS), as well as the geometrical structures of two C isomers (C(16), C(17)) and their corresponding chlorinated derivatives (C(16) Cl, C(17)Cl) which were newly purified have been investigated by the density functional theory (DFT). The variations of molecular structure, electronic structure and simulated spectra for C isomers after chlorination have been illustrated. Then, the above-mentioned C isomers and their chlorinated derivatives have been identified by the NEXAFS and XPS spectra which show the dependence on the local structure. Furthermore, we have also traced the source of the features in the total spectra by the spectral exploration of each component, which is very helpful for the further study of newly captured fullerene isomers and their derivatives. In this manuscript, we have performed first-principles simulation of the C1s X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure spectra (NEXAFS) for two C86 fullerene isomers and the related chlorinated species. The variations of molecular structure, electronic structure and simulated spectra for C86 isomers after chlorination have been illustrated. The above-mentioned C86 isomers and their chlorinated derivatives were identified by the NEXAFS and XPS spectra which show strong dependence on the local structure. Furthermore, we have also traced the source of the features in the total spectra by the spectral exploration of each component. The investigations on newly synthesized fullerenes and derivatives are effectively valuable and stimulative for the experimental researches in future. [ABSTRACT FROM AUTHOR]

We show here that the Hamiltonian for an electronic system may be written exactly in terms of fluctuation operators that transition constituent fragments between internally correlated states, accounting rigorously for inter-fragment electron exchange and charge transfer. Familiar electronic structure approaches can be applied to the renormalised Hamiltonian. For efficiency, the basis for each fragment can be truncated, removing high-energy local arrangements of electrons from consideration, and effectively defining collective coordinates for the fragments. For a large number of problems (especially for non-covalently interacting fragments), this has the potential to fold the majority of electron correlation into the effective Hamiltonian, and it should provide a robust approach to incorporating difficult electronic structure problems into large systems. The number of terms in the exactly transformed Hamiltonian formally scales quartically with system size, but this can be reduced to quadratic in the mesoscopic regime, to within an arbitrary error tolerance. Finally, all but a linear-scaling number of these terms may be efficiently decomposed in terms of electrostatic interactions between a linear-scaling number of pre-computed transition densities. In a companion article, this formalism is applied to an excitonic variant of coupled-cluster theory. [ABSTRACT FROM AUTHOR]

We introduce a new approach for analysing changes in electronic structure in the course of ab initio molecular dynamics simulations. The analysis is based on the time autocorrelation function of the many-body electronic wave-function. The approach facilitates the interpretation of dynamical events that may not be easily revealed by consideration of nuclear configurations alone. We apply the method to several illustrative examples: the shared proton vibration in the F−(H2O) complex, representing changes in strength of non-covalent interactions; proton transfer in the water dimer cation, as an example for chemical reactions in weakly bound systems; and the intramolecular proton transfer in malonaldehyde. In all cases, we observe distinct features in the time autocorrelation function when chemical changes occur. The autocorrelation function serves as an effective reaction coordinate, incorporating all degrees of freedom, including electronic ones. The method is also sensitive to changes in the electronic wave-function not accompanied by significant nuclear motions. [ABSTRACT FROM AUTHOR]

The adsorption properties of organic phosphines on transition metal (TM) surfaces (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) have been studied to explore the possibility of building novel heterogeneous chiral catalytic systems based on organic phosphines. Preferred adsorption sites, adsorption energies and surface electronic structures of a selected set of typical organic phosphines adsorbed on TM surfaces are calculated with density-functional theory to obtain a systematic understanding on the nature of adsorption interactions. All organic phosphines considered are found to chemically adsorb on these TM surfaces with the atop site as the most preferred one, and the TM-P bond is formed via the lone-pair electrons of the P atom and the directly contacted TM atom. These findings imply that it is indeed possible to build heterogeneous chiral catalytic systems based on organic phosphines adsorbed on TM surfaces, which, however, requires a careful design of molecular structure of organic phosphines. [ABSTRACT FROM AUTHOR]

A novel reduced-scaling, general-order coupled-cluster approach is formulated by exploiting hierarchical representations of many-body tensors, combined with the recently suggested formalism of scale-adaptive tensor algebra. Inspired by the hierarchical techniques from the renormalisation group approach, H/H2-matrix algebra and fast multipole method, the computational scaling reduction in our formalism is achieved via coarsening of quantum many-body interactions at larger interaction scales, thus imposing a hierarchical structure on many-body tensors of coupled-cluster theory. In our approach, the interaction scale can be defined on any appropriate Euclidean domain (spatial domain, momentum-space domain, energy domain, etc.). We show that the hierarchically resolved many-body tensors can reduce the storage requirements toO(N), whereNis the number of simulated quantum particles. Subsequently, we prove that any connected many-body diagram consisting of a finite number of arbitrary-order tensors, e.g. an arbitrary coupled-cluster diagram, can be evaluated inO(NlogN) floating-point operations. On top of that, we suggest an additional approximation to further reduce the computational complexity of higher order coupled-cluster equations, i.e. equations involving higher than double excitations, which otherwise would introduce a large prefactor into formalO(NlogN) scaling. [ABSTRACT FROM PUBLISHER]

The low-energy structures of Al8Sim(m= 1–6) have been determined by using the genetic algorithm combined with density functional theory and the Second-order Moller-Plesset perturbation theory (MP2) models. The results show that the close-packed structures are preferable in energy for Al–Si clusters and in most cases there exist a few isomers with close energies. The valence molecular orbitals, the orbital level structures and the electron localisation function (ELF) consistently demonstrate that the electronic structures of Al–Si clusters can be described by the jellium model. Al8Si4corresponds to a magic number structure with pronounced stability and large energy gap; the 40 valence electrons form closed 1S21P61D102S21F142P6shells. The ELF attractors also suggest weak covalent Si–Si, Si–Al and Al–Al bonding, and doping Si in aluminium clusters promotes the covalent interaction between Al atoms. [ABSTRACT FROM AUTHOR]