Showing papers on "Ab initio quantum chemistry methods published in 2012"
TL;DR: In this article, the synthesis of large-area, highly-crystalline monolayer N-doped graphene (NG) sheets via atmospheric-pressure chemical vapor deposition, yielding a unique Ndoping site composed of two quasi-adjacent substitutional nitrogen atoms within the same graphene sub-lattice (N2AA).
Abstract: Graphene is a two-dimensional network in which sp2-hybridized carbon atoms are arranged in two different triangular sub-lattices (A and B). By incorporating nitrogen atoms into graphene, its physico-chemical properties could be significantly altered depending on the doping configuration within the sub-lattices. Here, we describe the synthesis of large-area, highly-crystalline monolayer N-doped graphene (NG) sheets via atmospheric-pressure chemical vapor deposition, yielding a unique N-doping site composed of two quasi-adjacent substitutional nitrogen atoms within the same graphene sub-lattice (N2AA). Scanning tunneling microscopy and spectroscopy (STM and STS) of NG revealed the presence of localized states in the conduction band induced by N2AA-doping, which was confirmed by ab initio calculations. Furthermore, we demonstrated for the first time that NG could be used to efficiently probe organic molecules via a highly improved graphene enhanced Raman scattering.
601 citations
TL;DR: A methodology for the rigorous nonperturbative derivation of magnetic pseudospin Hamiltonians of mononuclear complexes and fragments based on ab initio calculations of their electronic structure is described and working expressions are derived for the pseudospIn Zeeman and zero-field splitting Hamiltonian corresponding to arbitrary pseudospins.
Abstract: A methodology for the rigorous nonperturbative derivation of magnetic pseudospin Hamiltonians of mononuclear complexes and fragments based on ab initio calculations of their electronic structure is described. It is supposed that the spin-orbit coupling and other relativistic effects are already taken fully into account at the stage of quantum chemistry calculations of complexes. The methodology is based on the establishment of the correspondence between the ab initio wave functions of the chosen manifold of multielectronic states and the pseudospin eigenfunctions, which allows to define the pseudospin Hamiltonians in the unique way. Working expressions are derived for the pseudospin Zeeman and zero-field splitting Hamiltonian corresponding to arbitrary pseudospins. The proposed calculation methodology, already implemented in the SINGLE_ANISO module of the MOLCAS-7.6 quantum chemistry package, is applied for a first-principles evaluation of pseudospin Hamiltonians of several complexes exhibiting weak, moderate, and very strong spin-orbit coupling effects.
502 citations
TL;DR: A methodology in which the use of additional characterization techniques, like single crystal magnetic measurements or luminescence experiments, complemented by relativistic ab initio calculations and a suitable choice of spin Hamiltonian models can be of great help to overcome difficulties in the rational design of lanthanide based Single Molecule Magnets with enhanced physical properties is exposed.
Abstract: Due to their usual large magnetic moments and large magnetic anisotropy lanthanide ions are investigated for the search of Single Molecule Magnets with high blocking temperature. However, the low symmetry crystal environment, the complexity of the electronic states or the non-collinearity of the magnetic anisotropy easy-axes in polynuclear systems make the rationalization of the magnetic behaviour of lanthanide based molecular systems difficult. In this perspective article we expose a methodology in which the use of additional characterization techniques, like single crystal magnetic measurements or luminescence experiments, complemented by relativistic ab initio calculations and a suitable choice of spin Hamiltonian models, can be of great help in order to overcome such difficulties, representing an essential step for the rational design of lanthanide based Single Molecule Magnets with enhanced physical properties.
353 citations
TL;DR: In this paper, a set of modified embedded-atom method (MEAM) potentials for the interactions between Al, Si, Mg, Cu, and Fe was developed from a combination of each element's MEAM potential in order to study metal alloying.
Abstract: A set of modified embedded-atom method (MEAM) potentials for the interactions between Al, Si, Mg, Cu, and Fe was developed from a combination of each element's MEAM potential in order to study metal alloying. Previously published MEAM parameters of single elements have been improved for better agreement to the generalized stacking fault energy (GSFE) curves when compared with ab initio generated GSFE curves. The MEAM parameters for element pairs were constructed based on the structural and elastic properties of element pairs in the NaCl reference structure garnered from ab initio calculations, with adjustment to reproduce the ab initio heat of formation of the most stable binary compounds. The new MEAM potentials were validated by comparing the formation energies of defects, equilibrium volumes, elastic moduli, and heat of formation for several binary compounds with ab initio simulations and experiments. Single elements in their ground-state crystal structure were subjected to heating to test the potentials at elevated temperatures. An Al potential was modified to avoid formation of an unphysical solid structure at high temperatures. The thermal expansion coefficient of a compound with the composition of AA 6061 alloy was evaluated and compared with experimental values. MEAM potential tests performed in this work, utilizing the universal atomistic simulation environment (ASE), are distributed to facilitate reproducibility of the results.
247 citations
TL;DR: The excitation spectrum of a Bose-Einstein condensate with cavity-mediated long-range interactions, which couple all particles to each other is investigated, finding a minimum was observed in the excitation energy, similar to that observed in roton excitations of the superfluid helium.
Abstract: Long-range interactions in quantum gases are predicted to give rise to an excitation spectrum of roton character, similar to that observed in superfluid helium. We investigated the excitation spectrum of a Bose-Einstein condensate with cavity-mediated long-range interactions, which couple all particles to each other. Increasing the strength of the interaction leads to a softening of an excitation mode at a finite momentum, preceding a superfluid-to-supersolid phase transition. We used a variant of Bragg spectroscopy to study the mode softening across the phase transition. The measured spectrum was in very good agreement with ab initio calculations and, at the phase transition, a diverging susceptibility was observed. The work paves the way toward quantum simulation of long-range interacting many-body systems.
228 citations
TL;DR: The exchange-hole dipole moment model of dispersion interactions of Becke and Johnson is implemented for calculations in solids using the pseudopotentials/plane-waves approach and retains the simplicity and efficiency of semilocal functionals while accurately treating dispersion interaction via a semiempirical asymptotic expansion.
Abstract: The exchange-hole dipole moment model of dispersion interactions of Becke and Johnson [J. Chem. Phys. 127 154108 (2007)] is implemented for calculations in solids using the pseudopotentials/plane-waves approach. The resulting functional retains the simplicity and efficiency of semilocal functionals while accurately treating dispersion interactions via a semiempirical asymptotic expansion. The dispersion coefficients are calculated completely ab initio using local quantities alone (density, gradient, Laplacian, and kinetic energy density). The two empirical parameters in the damping function are calculated by fit to a 65-molecule training set recalculated under periodic boundary conditions. Calculations in simple solids offer good results with minimal computational cost compared to electronic relaxation.
197 citations
TL;DR: A comprehensive investigation of on-the-fly surface-hopping simulations of 9H-adenine in the gas phase using different electronic structure theories (ab initio, semi-empirical, and density functional methods) shows discrepancies can always be traced back to topographical features of the underlying potential energy surfaces.
Abstract: In spite of the importance of nonadiabatic dynamics simulations for the understanding of ultrafast photo-induced phenomena, simulations based on different methodologies have often led to contradictory results. In this work, we proceed through a comprehensive investigation of on-the-fly surface-hopping simulations of 9H-adenine in the gas phase using different electronic structure theories (ab initio, semi-empirical, and density functional methods). Simulations that employ ab initio and semi-empirical multireference configuration interaction methods predict the experimentally observed ultrafast deactivation of 9H-adenine with similar time scales, however, through different internal conversion channels. Simulations based on time-dependent density functional theory with six different hybrid and range-corrected functionals fail to predict the ultrafast deactivation. The origin of these differences is analyzed by systematic calculations of the relevant reaction pathways, which show that these discrepancies can always be traced back to topographical features of the underlying potential energy surfaces. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731649]
192 citations
TL;DR: A chemical bonding model is developed, which allows the design of planar molecules with high coordination numbers, and shows that carbon occupies the peripheral position in aluminum-doped boron clusters rather than the center, because C is more electronegative than B and thus prefers to participate in localized 2c-2e s bonding, which is possible only at the circumference of the wheel structures.
Abstract: TaB10- and NbB10- clusters are produced in a laser-vaporization supersonic molecular beam cluster source and characterized by photoelectron spectroscopy.
181 citations
TL;DR: The authors' quantum chemical calculations on a high level of accuracy in a post-Hartree-Fock framework give excellent agreement with experiment and opens the door to reliable and detailed information on chemical interactions and the valence electronic structure in 3d transition-metal complexes also in transient excited electronic states.
Abstract: A new ab initio approach to the calculation of X-ray spectra is demonstrated. It combines a high-level quantum chemical description of the chemical interactions and local atomic multiplet effects. We show here calculated L-edge X-ray absorption (XA) and resonant inelastic X-ray scattering spectra for aqueous Ni2+ and XA spectra for a polypyridyl iron complex. Our quantum chemical calculations on a high level of accuracy in a post-Hartree–Fock framework give excellent agreement with experiment. This opens the door to reliable and detailed information on chemical interactions and the valence electronic structure in 3d transition-metal complexes also in transient excited electronic states. As we combine a molecular-orbital description with a proper treatment of local atomic electron correlation effects, our calculations uniquely allow, in particular, identifying the influence of interatomic chemical interactions versus intra-atomic correlations in the L-edge X-ray spectra.
164 citations
TL;DR: Based on an asymmetric Lanczos-chain subspace algorithm, damped coupled cluster linear response functions have been implemented for the hierarchy of coupled cluster (CC) models including CC with si....
Abstract: Based on an asymmetric Lanczos-chain subspace algorithm, damped coupled cluster linear response functions have been implemented for the hierarchy of coupled cluster (CC) models including CC with si ...
152 citations
TL;DR: In this article, the authors studied a promising lithium-ion conductor, garnet-type cubic Li oxides, at various Li concentrations and found two distinct mechanisms of Li-ion transport, with very different energy barriers and a strong dependence on Li distribution.
Abstract: We have studied a promising lithium-ion conductor, garnet-type cubic Li oxides, at various Li concentrations. The ab initio calculations performed on these materials revealed two distinct mechanisms of Li-ion transport, with very different energy barriers and a strong dependence on Li distribution. Our findings explain the origin of the vastly varying ionic conductivities at different Li concentrations and suggest possible principles to improve such materials for solid-state electrolyte applications.
TL;DR: The metal-doped B rings are established firmly as a new class of novel aromatic molecular wheels for transition-metal-centered nine-atom boron rings by chemical bonding analyses.
Abstract: We report the observation of two transition-metal-centered nine-atom boron rings, RhⓒB9– and IrⓒB9–. These two doped-boron clusters are produced in a laser-vaporization supersonic molecular beam and characterized by photoelectron spectroscopy and ab initio calculations. Large HOMO–LUMO gaps are observed in the anion photoelectron spectra, suggesting that neutral RhⓒB9 and IrⓒB9 are highly stable, closed shell species. Theoretical calculations show that RhⓒB9 and IrⓒB9 are of D9h symmetry. Chemical bonding analyses reveal that these complexes are doubly aromatic, each with six completely delocalized π and σ electrons, which describe the bonding between the central metal atom and the boron ring. This work establishes firmly the metal-doped B rings as a new class of novel aromatic molecular wheels.
TL;DR: In this article, the authors demonstrate the existence of a 3D hole conductive network in these ternary diamond-like Cu${}_{2}$Sn${X}_{3}$ ($X$ $=$ Se, S) semiconductors using ab initio calculations, and identify the features of the electronic structure responsible for this good performance.
Abstract: The $p$-type Cu${}_{2}$Sn${X}_{3}$ ($X$ $=$ Se, S) compounds are known experimentally to be good thermoelectric materials, although the reasons for this good performance in an adamantine-derived crystal structure are not well understood. Here, we demonstrate the existence of a three-dimensional (3D) hole conductive network in these ternary diamondlike Cu${}_{2}$Sn${X}_{3}$ ($X$ $=$ Se, S) semiconductors using ab initio calculations, and identify the features of the electronic structure responsible for this good performance. We also provide results as a function of doping level to find the regime where the highest performance will be realized and estimate the maximum figure of merit, $ZT$. Our results clearly show that the strong hybridization between 3$d$ orbitals from copper and $p$ orbitals from selenium or sulfur at the upper valence band leads to the 3D $p$-type hole transport channel, mainly consisting of Cu-$X$ and $X$-$X$ networks in Cu${}_{2}$Sn${X}_{3}$ ($X$ $=$ Se, S). The resulting heavy, but still conductive, hybridized bands of Cu $d$--chalcogen $p$ character are highly favorable for thermoelectric performance. The electrical transport properties of these $p$-type materials are mainly determined by these bands and have been investigated by Boltzmann transport methods. The optimal doping levels of Cu${}_{2}$Sn${X}_{3}$ are estimated to be around 0.1 holes per unit cell at 700 K. The theoretical figure of merit $ZT$ has been predicted.
TL;DR: A hierarchy of self-consistent GW methods, starting from non-selfconsistent, through partial selfconsistency in the eigenvalues and in the Green's function (sc$G{W}_{0}$), is presented in this article.
Abstract: Many-body perturbation theory in the $GW$ approximation is a useful method for describing electronic properties associated with charged excitations. A hierarchy of $GW$ methods exists, starting from non-self-consistent ${G}_{0}$${W}_{0}$, through partial self-consistency in the eigenvalues and in the Green's function (sc$G{W}_{0}$), to fully self-consistent $GW$ (sc$GW$). Here, we assess the performance of these methods for benzene, pyridine, and the diazines. The quasiparticle spectra are compared to photoemission spectroscopy (PES) experiments with respect to all measured particle removal energies and the ordering of the frontier orbitals. We find that the accuracy of the calculated spectra does not match the expectations based on their level of self-consistency. In particular, for certain starting points ${G}_{0}$${W}_{0}$ and sc$G{W}_{0}$ provide spectra in better agreement with the PES than sc$GW$.
TL;DR: The formalism and first implementation of the ab initio multiconfigurational Ehrenfest (AI-MCE) method for simulation of ultrafast nonadiabatic dynamics, which uses the MOLPRO electronic structure program to calculate the potential energy surfaces on the fly.
Abstract: In this article we report the formalism and first implementation of the ab initio multiconfigurational Ehrenfest (AI-MCE) method for simulation of ultrafast nonadiabatic dynamics, which uses the MOLPRO electronic structure program to calculate the potential energy surfaces on the fly. The approach is tested on the benchmark of the excited ππ* state dynamics of ethylene producing the dynamics which agree with previous simulations by ab initio multiple spawning technique. The AI-MCE seems to be robust, stable and efficient.
TL;DR: In this paper, structural, electronic, and optical properties for cubic, tetragonal, and monoclinic crystalline phases of ZrO2, as derived from it ab initio full-relativistic calculations, are presented.
Abstract: Structural, electronic, and optical properties for the cubic, tetragonal, and monoclinic crystalline phases of ZrO2, as derived from it ab initio full-relativistic calculations, are presented. The electronic structure calculations were carried out by means of the all-electron full potential linear augmented plane wave method, within the framework of the density functional theory and the local density approximation. The calculated carrier effective masses are shown to be highly anisotropic. The results obtained for the real and imaginary parts of the dielectric function, the reflectivity, and the refraction index, show good agreement with the available experimental results. In order to obtain the static dielectric constant of ZrO2, we added to the electronic part, the optical phonons contribution, which leads to values of e1(0)~29.5, 26.2, 21.9, respectively along the xx, yy, and zz directions, for the monoclinic phase, in excellent accordance with experiment. Relativistic effects, including the spin-orbit interaction, are demonstrated to be important for a better evaluation of the effective mass values, and in the detailed structure of the frequency dependent complex dielectric function.
TL;DR: In this article, the elastic response of nine binary early transition metal nitrides (ScN, TiN, VN, YN, ZrN, NbN, LaN, HfN, and TaN) and AlN were studied.
Abstract: Motivated by an increasing demand for coherent data that can be used for selecting materials with properties tailored for specific application requirements, we studied elastic response of nine binary early transition metal nitrides (ScN, TiN, VN, YN, ZrN, NbN, LaN, HfN, and TaN) and AlN. In particular, single-crystal elastic constants, Young's modulus in different crystallographic directions, polycrystalline values of shear and Young's moduli, and the elastic anisotropy factor were calculated. Additionally, we provide estimates of the third order elastic constants for the ten binary nitrides.
TL;DR: A fully analytical method for calculating Born charges and, hence, infrared intensities of periodic systems, is formulated and implemented in the CRYSTAL program, which uses a local gaussian type basis set.
Abstract: A fully analytical method for calculating Born charges and, hence, infrared intensities of periodic systems, is formulated and implemented in the CRYSTAL program, which uses a local Gaussian type basis set. Our efficient formalism combines integral gradients with first-order coupled perturbed Hartree–Fock/Kohn Sham electronic response to an electric field. It avoids numerical differentiation with respect to wave vectors, as in some Berry phase approaches, and with respect to atomic coordinates. No perturbation equations for the atomic displacements need to be solved. Several tests are carried out to verify numerical stability, consistency in one, two, and three dimensions, and applicability to large unit cells. Future extensions to piezoelectricity and Raman intensities are noted.
TL;DR: Comparison with experimental scanning tunneling microscopy images, dI/dV curves, and cluster heights proves that C(21) is the experimentally observed dominating C precursor in graphene chemical vapor deposition (CVD) growth.
Abstract: Ground-state structures of supported C clusters, CN (N = 16, ..., 26), on four selected transition metal surfaces [Rh(111), Ru(0001), Ni(111), and Cu(111)] are systematically explored by ab initio calculations. It is found that the core–shell structured C21, which is a fraction of C60 possessing three isolated pentagons and C3v symmetry, is a very stable magic cluster on all these metal surfaces. Comparison with experimental scanning tunneling microscopy images, dI/dV curves, and cluster heights proves that C21 is the experimentally observed dominating C precursor in graphene chemical vapor deposition (CVD) growth. The exceptional stability of the C21 cluster is attributed to its high symmetry, core–shell geometry, and strong binding between edge C atoms and the metal surfaces. Besides, the high barrier of two C21 clusters’ dimerization explains its temperature-dependent behavior in graphene CVD growth.
TL;DR: It is suggested that the potential energy surface construction is more appropriately regarded as a legitimate and effective modification of quantum mechanics for chemical purposes.
Abstract: Transition state theory was introduced in 1930s to account for chemical reactions. Central to this theory is the idea of a potential energy surface (PES). It was assumed that such a surface could be constructed using eigensolutions of the Schrodinger equation for the molecular (Coulomb) Hamiltonian but at that time such calculations were not possible. Nowadays quantum mechanical ab initio electronic structure calculations are routine and from their results PESs can be constructed which are believed to approximate those assumed derivable from the eigensolutions. It is argued here that this belief is unfounded. It is suggested that the potential energy surface construction is more appropriately regarded as a legitimate and effective modification of quantum mechanics for chemical purposes.
TL;DR: The structures and the delocalized bonding of the two lowest lying isomers of B(21)(-) were found to be similar to those in the two low energy isomers in B(19)(-).
Abstract: The structures and chemical bonding of the B21− cluster have been investigated by a combined photoelectron spectroscopy and ab initio study The photoelectron spectrum at 193 nm revealed a very high adiabatic electron binding energy of 438 eV for B21− and a congested spectral pattern Extensive global minimum searches were conducted using two different methods, followed by high-level calculations of the low-lying isomers The global minimum of B21− was found to be a quasiplanar structure with the next low-lying planar isomer only 19 kcal/mol higher in energy at the CCSD(T)/6-311-G* level of theory The calculated vertical detachment energies for the two isomers were found to be in good agreement with the experimental spectrum, suggesting that they were both present experimentally and contributed to the observed spectrum Chemical bonding analyses showed that both isomers consist of a 14-atom periphery, which is bonded by classical two-center two-electron bonds, and seven interior atoms in the planar str
TL;DR: Measurement of state-resolved inelastic scattering cross sections for collisions between two open-shell molecules that are both prepared in a single quantum state reveals the crucial role of electrostatic forces in complex molecular collision processes.
Abstract: Whereas atom-molecule collisions have been studied with complete quantum-state resolution, interactions between two state-selected molecules have proven much harder to probe. Here, we report the measurement of state-resolved inelastic scattering cross sections for collisions between two open-shell molecules that are both prepared in a single quantum state. Stark-decelerated hydroxyl (OH) radicals were scattered with hexapole-focused nitric oxide (NO) radicals in a crossed-beam configuration. Rotationally and spin-orbit inelastic scattering cross sections were measured on an absolute scale for collision energies between 70 and 300 cm−1. These cross sections show fair agreement with quantum coupled-channels calculations using a set of coupled model potential energy surfaces based on ab initio calculations for the long-range nonadiabatic interactions and a simplistic short-range interaction. This comparison reveals the crucial role of electrostatic forces in complex molecular collision processes.
TL;DR: The orbital-adaptive time-dependent coupled-cluster (ATCC) method as mentioned in this paper is a hierarchy of approximations to the now standard multi-configurational Hartree method for fermions.
Abstract: The curse of dimensionality (COD) limits the current state-of-the-art ab initio propagation methods for non-relativistic quantum mechanics to relatively few particles. For stationary structure calculations, the coupled-cluster (CC) method overcomes the COD in the sense that the method scales polynomially with the number of particles while still being size-consistent and extensive. We generalize the CC method to the time domain while allowing the single-particle functions to vary in an adaptive fashion as well, thereby creating a highly flexible, polynomially scaling approximation to the time-dependent Schrodinger equation. The method inherits size-consistency and extensivity from the CC method. The method is dubbed orbital-adaptive time-dependent coupled-cluster, and is a hierarchy of approximations to the now standard multi-configurational time-dependent Hartree method for fermions. A numerical experiment is also given.
Posted Content•
TL;DR: A new model is introduced, HBB2-pol, which is capable of accurately mapping CCSD(T) results for water dimers and trimers into an efficient analytical function and is further established through comparison with the experimentally determined second and third virial coefficients.
Abstract: The microscopic behavior of water under different conditions and in different environments remains the subject of intense debate. A great number of the controversies arise due to the contradictory predictions obtained within different theoretical models. Relative to conclusions derived from force fields or density functional theory, there is comparably less room to dispute highly-correlated electronic structure calculations. Unfortunately, such ab initio calculations are severely limited by system size. In this study, a detailed analysis of the two- and three-body water interactions evaluated at the CCSD(T) level is carried out to quantitatively assess the accuracy of several force fields, density functional theory, and ab initio-based interaction potentials that are commonly used in molecular simulations. Based on this analysis, a new model, HBB2-pol, is introduced which is capable of accurately mapping CCSD(T) results for water dimers and trimers into an efficient analytical function. The accuracy of HBB2-pol is further established through comparison with the experimentally determined second and third virial coefficients.
TL;DR: The results support the idea that binaryucleation of sulfuric acid and water cannot account for nucleation of sulphuric acid in the lower troposphere.
Abstract: The role of the binary nucleation of sulfuric acid in aerosol formation and its implications for global warming is one of the fundamental unsettled questions in atmospheric chemistry. We have investigated the thermody- namics of sulfuric acid hydration using ab initio quantum mechanical methods. For H2SO4(H2O)n where n =1 −6, we used a scheme combining molecular dynamics configurational sampling with high-level ab initio calculations to locate the global and many low lying local minima for each cluster size. For each isomer, we extrapolated the Moller−Plesset perturbation theory (MP2) energies to their complete basis set (CBS) limit and added finite temperature corrections within the rigid-rotor-harmonic-oscillator (RRHO) model using scaled harmonic vibrational frequencies. We found that ionic pair (HSO4 − ·H3O + )(H2O)n−1 clusters are competitive with the neutral (H2SO4)(H2O)n clusters for n ≥ 3 and are more stable than neutral clusters for n ≥ 4 depending on the temperature. The Boltzmann averaged Gibbs free energies for the formation of H2SO4(H2O)n clusters are favorable in colder regions of the troposphere (T = 216.65−273.15 K) for n =1 −6, but the formation of clusters with n ≥ 5 is not favorable at higher (T > 273.15 K) temperatures. Our results suggest the critical cluster of a binary H2SO4−H2O system must contain more than one H2SO4 and are in concert with recent findings 1 that the role of binary nucleation is small at ambient conditions, but significant at colder regions of the troposphere. Overall, the results support the idea that binary nucleation of sulfuric acid and water cannot account for nucleation of sulfuric acid in the lower troposphere.
TL;DR: The definition and testing of a new ab initio 12-dimensional potential for the water dimer with flexible monomers is reported, and an adiabatic scheme has been invoked in order to decouple fast (intramolecular) modes and slow (intermolescular) ones.
Abstract: We report the definition and testing of a new ab initio 12-dimensional potential for the water dimer with flexible monomers. Using our recent accurate CCpol-8s rigid water pair potential [W. Cencek, K. Szalewicz, C. Leforestier, R. van Harrevelt, and A. van der Avoird, Phys. Chem. Chem. Phys. 10, 4716 (2008)10.1039/b809435g] as a reference for the undistorted monomers’ geometries, a distortion correction has been added, which was taken from a former flexible-monomer ab initio potential. This correction allows us to retrieve the correct binding energy De=21.0 kJ mol −1, and leads to an equilibrium geometry in close agreement with the one obtained from benchmark calculations. The kinetic energy operator describing the flexible-monomer water dimer has been expressed in terms of Radau coordinates for each monomer and a recent general cluster polyspherical formulation describing their relative motions. Within this formulation, an adiabatic scheme has been invoked in order to decouple fast (intramolecular) mode...
TL;DR: Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S(1) (ππ*) excited state of phenol, catechol, resorcinol, and hydroquinone following excitation at 267 nm, and observe rapid (<1 ps) intramolecular vibrational redistribution on the S( 1) potential surface.
Abstract: Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S(1) (ππ*) excited state of phenol (hydroxybenzene), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene) following excitation at 267 nm. Our analysis was supported by ab initio calculations at the coupled-cluster and CASSCF levels of theory. In all cases, we observe rapid (<1 ps) intramolecular vibrational redistribution on the S(1) potential surface. In catechol, the overall S(1) state lifetime was observed to be 12.1 ps, which is 1-2 orders of magnitude shorter than in the other three molecules studied. This may be attributed to differences in the H atom tunnelling rate under the barrier formed by a conical intersection between the S(1) state and the close lying S(2) (πσ*) state, which is dissociative along the O-H stretching coordinate. Further evidence of this S(1)/S(2) interaction is also seen in the time-dependent anisotropy of the photoelectron angular distributions we have observed. Our data analysis was assisted by a matrix inversion method for processing photoelectron images that is significantly faster than most other previously reported approaches and is extremely quick and easy to implement.
TL;DR: Experiments revealed that small boron cluster anions and cations are (quasi-)planar, and chemical bonding analysis given by AdNDP reveals that the B(14) cage is an all-boron fullerene with 18 delocalized σ-electrons following the 2(n+1)(2) rule of spherical aromaticity.
Abstract: Experiments revealed that small boron cluster anions and cations are (quasi-)planar. For neutral boron cluster, (quasi-)planar motifs are also suggested to be global minimum by many theoretical studies, and a structural transformation from quasi-planar to double-ring tubular structures occurs at B20. However, a missing opportunity is found for neutral B14, which is a flat cage and more stable than the previous quasi-planar one by high level ab initio calculations. The B14 cage has a large HOMO-LUMO gap (2.69 eV), and NICS values reveal that it is even more aromatic than the known most aromatic quasi-planar B12 and double-ring B20, which indicates a close-shell electronic structure.Chemical bondinganalysis given by AdNDP reveals that the B14 cage is an all-boron fullerene with 18 delocalized σ-electrons following the 2(n+1)2 rule of spherical aromaticity. The geometry and bonding features of the B14 cage are unique denying conversional thinking.
TL;DR: In this article, laser-driven shock wave measurements on hydrogen and deuterium precompressed in diamond anvil cells from 0.16 to 1.6 GPa provide new shock Hugoniot data over a significantly broader range of density-temperature phase space than was previously achievable.
Abstract: Laser-driven shock wave measurements on hydrogen and deuterium precompressed in diamond anvil cells from 0.16 to 1.6 GPa provide new shock Hugoniot data over a significantly broader range of density-temperature phase space than was previously achievable. Observations of shock velocity and thermal emission provide complete equation of state data (pressure, density, internal energy, and temperature) in the dense fluid regime up to 175 GPa. This data set is used to benchmark recent advanced ab initio calculations and is seen to be in good agreement with a maximum $8%$ density difference above 100 GPa. Thermodynamic quantities (specific heat and Gruneisen coefficient) are calculated directly from the data and compared to theory. Optical reflectivity data show a continuous transition from an electrically insulating to conducting fluid state and reveal that this transition is increasingly sensitive to temperature with increasing density. Ab initio calculations are observed to underestimate the temperature onset of metallization.
TL;DR: In this paper, an orthorhombic carbon (O$-carbon) in $Pbam$ (${D}_{2h}^{9}$) symmetry was identified for compressed graphite in AA stacking, which is formed via a distinct one-layer by one layer slip and buckling mechanism along the [210] direction.
Abstract: We identify by ab initio calculations an orthorhombic carbon ($O$-carbon) in $Pbam$ (${D}_{2h}^{9}$) symmetry for compressed graphite in AA stacking, which is formed via a distinct one-layer by one-layer slip and buckling mechanism along the [210] direction. It is dynamically stable and energetically more favorable than other known compressed graphite phases, albeit its slightly higher kinetic barrier. The $O$-carbon is comparable to diamond in ultralow compressibility, has a band gap wider than that of diamond, and is compatible with experimental x-ray diffraction data. The present results offer insights for understanding the complex structural landscape of compressed graphite and the versatile nature of carbon in forming a rich variety of structures under pressure.