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The electron correlation effects covered by density functional theory (DFT) can be assessed qualitatively by comparing DFT densities ρ(r) with suitable reference densities obtained with wavefunction theory (WFT) methods that cover typical electron correlation effects. The analysis of difference densities ρ(DFT)-ρ(WFT) reveals that LDA and GGA exchange (X) functionals mimic non-dynamic correlation effects in an unspecified way. It is shown that these long range correlation effects are caused by the self-interaction error (SIE) of standard X functionals. Self-interaction corrected (SIC) DFT exchange gives, similar to exact exchange, for the bonding region a delocalized exchange hole, and does not cover any correlation effects. Hence, the exchange SIE is responsible for the fact that DFT densities often resemble MP4 or MP2 densities. The correlation functional changes X-only DFT densities in a manner observed when higher order coupling effects between lower order N-electron correlation effects are included. Hybrid functionals lead to changes in the density similar to those caused by SICDFT, which simply reflects the fact that hybrid functionals have been developed to cover part of the SIE and its long range correlation effects in a balanced manner. In the case of spin-unrestricted DFT (UDFT), non-dynamic electron correlation effects enter the calculation both via the X functional and via the wavefunction, which may cause a double-counting of correlation effects. The use of UDFT in the form of permuted orbital and broken-symmetry DFT (PO-UDFT, BS-UDFT) can lead to reasonable descriptions of multireference systems provided certain conditions are fulfilled. More reliable, however, is a combination of DFT and WFT methods, which makes the routine description of multireference systems possible. The development of such methods implies a separation of dynamic and non-dynamic correlation effects. Strategies for accomplishing this goal are discussed in general and tested in practice for CAS (complete active space)-DFT. [ABSTRACT FROM AUTHOR]

Oxidative decomposition of solid lithium peroxide is an important part of the charging process in a Li-O2 battery. In this paper, we investigate oxidative decomposition mechanisms of lithium peroxide clusters as molecular models for solid lithium peroxide using density functional methods to understand charging processes in advanced energy storage systems. Most calculations are done using a (Li2O2)4 cluster with similar results obtained from a larger (Li2O2)16 cluster. Reaction pathways of the clusters involving different sequences of oxidation, oxygen evolution, lithium cation removal, and spin excitation are investigated. The computations suggest that certain oxidative decomposition routes may not have dependence on the oxygen evolution or Li-ion removal kinetics due to the exothermicity of oxygen removal and Li+ removal (by solvent) upon oxidation. The computed charge potentials evaluated using a tetramer model indicates that it is possible to have low overcharge potential provided there exists a good electronic conductivity to facilitate the oxidative decomposition. Finally, oxidation potentials of a series of LixOy clusters are investigated to assess their dependence on stoichiometry and how the local site from which the electrons are being removed affects the charge potentials. [ABSTRACT FROM AUTHOR]

Knowledge of the structure of simple fluids in nano-tubes constitutes important information in many scientific and technical branches. Computer simulations and density functional theory (DFT) offer accurate but laborious results. We have proposed a simple analytical method to determine the background correlation function on the basis of the residual chemical potentials of a pair of interacting bodies and of the corresponding combined body. These potentials are obtained in terms of geometric quantities. In this paper we dealt with the combination rule for the geometric quantity Q; the harmonic mean rule was proposed and verified at low densities by calculating the third cross-virial coefficient, and by comparing calculated density profiles of the inhomogeneous systems of hard sphere-wall at higher densities. A slight improvement over the previous results were found. Next, we applied our analytic method to realistic systems of a simple molecule in the graphite cylindrical pore. Hydrogen (and carbon monoxide), interacting with carbon of the graphite via the modified LJ potential are considered and the density profile was determined taking into account only the soft-sphere interaction within Weeks-Chandler-Andersen approximation. The considered approach was found to yield a fair description of the realistic simple fluid-cylindrical pore system. [ABSTRACT FROM AUTHOR]

The Becke three-parameter Lee-Yang-Parr (B3LYP) density functional method is applied to the study of the reaction Li + HF H + LiF; the results obtained are compared with experiment and previous multireference singles and doubles configuration interaction (MRDCI) calculations, and with singles and doubles quadratic configuration interaction (QCISD) and Gaussian 2 (G2) model chemistry calculations performed also in this paper. It is found that, using an extended 6-311 + G(3df,3pd) basis set, the predicted stabilization enthalpy of the initial LiFH complex (- 34.6 kJ mol-1) and the exoergicity of the reaction (-7.3 kJ mol-1) are predicted in agreement with experiment (~ - 31 kJ mol-1 and - 4.8 +/- 8 kJ mol-1, respectively). These results are also in agreement with the MRDCI calculations (~ - 31.5 kJ mol-1 and - 9 kJ mol-1, respectively). However, the energy of the transition state with respect to the reactants at the B3LYP level is about 25 kJ mol-1 lower than the MRDCI result (which agrees with the QCISD and G2 values). Therefore, it is concluded that B3LYP is not describing this reaction properly. It is shown, however, that this defect is due mainly to the inclusion of the LYP correlation functional instead of the Perdew-Wang originally considered by Becke for developing his adiabatically connected functional. When B3PW91 is considered instead of B3LYP, the height of the transition state is in better agreement with the conventional ab initio methods, although still off by 50%. [ABSTRACT FROM AUTHOR]

This paper presents the definition and characterisation of quantum molecular polyhedra. They are taken here within the description of a single molecule, using quantum molecular orbital (MO) density functions as vertices. The formalism and parameters associated to these mathematical structures are analysed. Picture Drawn by Pep Camps, Girona (2015). [ABSTRACT FROM PUBLISHER]

In a recent publication, Lobsiger et al. [Phys. Chem. Chem. Phys. 12, 5032 (2010)] presented infrared and electronic absorption spectra of supersonic jet-cooled 5-methyl-2-hydroxypyrimidine (5M2HP), the enol form of deoxythymine. In addition, they reported on the fast nonradiative decay of the S1 population to a dark state. In the present paper, we have investigated the mechanism and rate constants of this nonradiative decay by means of quantum chemical multi-configuration methods. To this end, minima of the lowest excited singlet and triplet states as well as the minimum-energy crossing point of singlet and triplet potential energy hypersurfaces (PEHs) have been determined employing a numerical DFT/MRCI gradient where DFT/MRCI stands for a combination of density functional theory (DFT) and a semi-empirical multi-reference configuration interaction (MRCI) approach. Rate constants have been calculated in the Condon approximation using a time-dependent approach based on harmonic oscillator functions and electronic spin–orbit coupling matrix elements evaluated at the DFT/MRCI level. It is shown that the first excited triplet state possesses 3(n → π*) character in the gas phase. Fast intersystem crossing is mediated by the low-lying 3(π → π*) state whose PEH crosses both, the S1 1(n → π*) and T1 3(n → π*) PEHs. [ABSTRACT FROM AUTHOR]

In this paper the aggregates of the chiral organolithium N-Boc-2-lithiopiperidine [Boc=CO2C(CH3)3], which play an important role in the formation of chiral 2-substituted piperidines found in many alkaloid structures and medicinal compounds, have been investigated within the framework of Density Functional Theory (DFT) calculations. In the complex structures, the lithium atoms are tetra-coordinated, the diaminoalkoxide ligand is tridentate to one lithium atom and forms a chelate with the substrate which is stabilized by the solvent diethyl ether. The same type of bonding was observed for all the different ligand-bound structures; for ligands 6 and 7, which have bulky substituents, selectivity was in agreement with experiment. The results shed light on the microscopic structures of these species and suggest a potential ligand, 11, to yield high enantioselectivity. [ABSTRACT FROM AUTHOR]

The direct correlation function (DCF) plays an important role in liquid integral-equation theories and non-mean-field applications of the classical density functional theory (DFT). While for a simple fluid the DCF can easily be calculated from the radial distribution function via the Fourier transform and/or, for special cases, can be derived from analytical solutions of the Ornstein–Zernike equation, computation of the site–site DCFs of a molecular fluid is more challenging because of numerical issues associated with solving the matrix integral equations. This paper describes a new theoretical method for accurate evaluation of the site–site DCFs of molecular fluids by combination of molecular simulation and analytical asymptotic analysis. The computational procedure entails four steps: (1) molecular simulation is used to calculate the site–site total correlation functions (TCFs) in real space; (2) the reference-interaction-site model (RISM) is used to calculate the site–site DCFs in Fourier space at large wavenumbers; (3) asymptotic expressions are derived for the TCFs and DCFs in the limit of small wavenumbers; and (4) site–site DCFs over the entire range are obtained by interpolation of the asymptotic results. The numerical procedure has been illustrated by application to bulk SPC/E water. Accurate evaluation of the site–site DCFs for water lays a foundation for future applications of the DFT to aqueous systems with atomic details. [ABSTRACT FROM PUBLISHER]

The paper reports Time Dependent Density Functional Theory (TD DFT) calculations providing the structure, electronic properties and spectra of [Ru(II)(bpy)3− n (dcbpy) n ]2+ and [Rh(III)(bpy)3− n (dcbpy) n ]3+ complexes, where bpy = 2,2′-bipyridyl, dcbpy = 4,4′-dicarboxy-2,2′-bipyridyl, and n = 0, 1, 2, 3, studied as possible pigments for dye-sensitized solar cells. The role of the metallic ion and of the COOH groups on the optical properties of these complexes are compared and contrasted and their relevance as dyes for hybrid organic–inorganic photovoltaic cells is discussed. It was found that the optical spectra are strongly influenced by the metallic ion, with visible absorption bands for the Ru(II) complexes and only ultraviolet bands for the Rh(III) complexes. Upon excitation, the extra positive charge of the Rh3+ centre tends to draw electrons towards the metal ion, facilitating some charge transfer from the ligand to the metal, whereas in the case of the Ru2+ ion the electron transfer is clearly from the metal to the ligand. The carboxyl groups play an important role in strengthening the absorption bands in solution in the visible region. Of the complexes studied, the most suited as pigments for dye-sensitized solar cells are the [Ru(II)(bpy)3− n (dcbpy) n ]2+ complexes with n = 1 and 2. This is based on the following arguments: (i) their intense absorption band in the visible region, (ii) the presence of the anchoring groups allowing the bonding to the TiO2 substrate and the charge transfer, and (iii) the good energy level alignment with the conduction band edge of the semiconducting substrate and the redox level of the electrolyte. [ABSTRACT FROM PUBLISHER]

The contributions of John C. Slater and his students to the development of quantum theory of molecules and solids have often been overlooked, especially in the area of the early computer calculations using approximations which were the predecessor to Density Functional Theory. This paper looks back to the early days of the Quantum Theory Project, when Professor Slater was heavily involved, and acknowledges research in this area which laid the foundations to the theory which has become one of the premier approximations in quantum theory today. [ABSTRACT FROM AUTHOR]

Semi-local density functional theory suggests a connection between static correlation and self-interaction. It is difficult to make such a connection from the wave function theory perspective, since few wave function methods permit self-interaction error. However, the random phase approximation for ground-state correlation, which has a wave function derivation, does include self-interaction in its direct (Hartree) variant. This variant also describes left-right correlation. The self-interaction can be removed by means of second-order screened exchange; however, this also has negative consequences for the description of static correlation. This paper discusses the connection between the two concepts (static correlation and self-interaction) from the perspective provided by the random phase approximation. [ABSTRACT FROM AUTHOR]

Glasses of the system xGd2O3 · (100 - x)[7GeO2 · 3PbO] with 0 ≤ x ≤ 40 mol% were prepared using the melt quenching method. Lead germanate glasses are particularly interesting in the context of the germanate anomaly. In this paper, we investigate changes in the coordination number of germanium in gadolinium-lead germanate glasses using molar volume analysis, density measurements, FTIR and UV-VIS spectroscopy, and density functional theory (DFT). Despite some inconsistencies, the coordination change model remains the currently accepted model for the anomalous behaviour of lead germanate glasses. Based on these experimental results, we propose the following mechanism for the germanate anomaly. (i) The low thermodynamic stability of the [GeO6] structural unit and the occupation of interstices of larger dimensions (the six-coordinated interstices of the [PbO6] structural units) in the lead germanate network yield [GeO5] structural units with higher thermodynamic stability and larger ionic radii. (ii) Not linked to the terminal oxygens of the [GeO5] structural units and with the formation of smaller network cavities of the lead germanate glass, links are required with [GeO4] tetrahedra for stabilization, generating the formation of three-membered rings of [GeO4] tetrahedral structural units. [ABSTRACT FROM AUTHOR]

Computational results on collisional energy transfer between excited and cold azulene and Ar are reported under initial conditions similar to those of crossed molecular beam experiments (Liu, Hsu, Lyu and Ni, J. Chem. Phys. 125 204309 (2006)). The in-plane scattering cross-section is asymmetric with a preference for positive angles. The out-of-plane scattering angle is symmetric in both positive and negative angles with a strong forward scattering peak. In both T → V/R dominates over V → R/T. The double differential cross-section shows a high probability for forward, then sideways and finally, backward scattering. The latter shows relatively high probability for supercollisions. Average energy transfer quantities and collisional energy transfer probability density functions, P(E,E'), are presented and results for Ar and Kr as colliders are compared. At low initial relative translational energies the up-collision branch of P(E,E') shows a peak. This peak, which is absent at higher relative translational energies, is due to the formation of a collision complex. Special attention is paid to the role of rotational energy in the energy transfer process. Changing the rotational temperature from 0.5 K to 2000 K changes the percentage of up and down collisions as well as the values of the average energy transferred quantities. The effect of the translational energy on energy transfer is discussed. There is broad agreement between experiment and computation. [ABSTRACT FROM AUTHOR]

The paper reports calculations on binuclear manganese(II) clusters related to those found in biological systems. B3LYP/6-311g(d,p) density functional theory (DFT) calculations are carried out specifically on a set of clusters that derive from the X-ray crystal structure of DNA polymerase β [Batra, V. K. et al., Structure 14, 757-766 (2006)]. Issues investigated are: (a) the relative energy of the lowest and highest spin states (antiferromagnetic (low spin/broken symmetry = LS/BS) or ferromagnetic); (b) the Mn(II)-Mn(II) distance; (c) the effect of water versus CH3OH (a sugar analogue) as a direct Mn ligand; and (d) the effect of the kind of oxygen bridge (mono-oxygen, single-oxygen from a carboxylate or phosphate, or a two-oxygen bridge from a carboxylate), on the geometry and energy. It was found generally that the antiferromagnetic state is lower in energy, that the Mn(II)-Mn(II) distance (which varies from 2.91 to 3.57 Å in the series studied) is longer for ferromagnetic states than for the corresponding low spin states, that the interchange of CH3OH and water does not affect the results, and that a single (carboxylate) oxygen as bridge leads to a lower energy than a corresponding two (carboxylate) oxygen bridge, as well as to a more compact structure. [ABSTRACT FROM AUTHOR]

In a series of papers, we have used a field theoretical description of the liquid state for a study of ionic systems. The formalism constructed is based on a simple Hamiltonian including the interaction potential and the ideal entropy. We discuss and analyse the Hamiltonian by detailing the role of its different contributions and its physical content. We show that the simple Hamiltonian based on particle densities as the fields also reproduces exactly the usual liquid state theory formulated in a discrete particle description rather than continuous fields. In this perspective, the formalism is discussed in view of a well-known exact and fundamental relation of the liquid state theory: the contact theorem. We demonstrate the validity of this theorem within the field theoretical framework. We find that the specific form of the Hamiltonian, in particular of the ideal entropy functional, is essential. The analysis of this term shows that it introduces the basic principle of uncertainty and the principle of the indiscernibility of quantum physics which exists for particles in a way suited for a description in terms of fields. This discussion is illustrated in the case of an ionic solution at an interface. [ABSTRACT FROM AUTHOR]

Ab initio and density functional theory calculations are presented of the structures and vibrational properties of the weakly-bound hydrogen-bonded species, (NH3)2 and (PH3)2. Earlier studies of the ammonia dimer have indicated that the structure of the most stable species, and the question of whether a particular structure is a genuine minimum or a transition state, is largely determined by the combination of the theory employed and the basis set used. This paper explores the performance of a variety of basis sets, used in conjunction with second-order Møller–Plesset perturbation theory (MP2), and with density functional theory (DFT), in an attempt to achieve convergence on the most favourable structures of these two aggregates. The ammonia dimer is found to contain a linear hydrogen bond in the eclipsed conformation, while the phosphine dimer is characterized by a blue-shifting hydrogen bond, in a centrosymmetric doubly bifurcated structure. [ABSTRACT FROM AUTHOR]

It has been suggested that electronic excited states outside of those included within the Gouterman four-orbital model (Qy, Qx, Bx, and By) are present in the low-energy region of chlorophyll molecules. In particular, studies performed using time-dependent density functional theory (TDDFT) predict the presence of a very large number of such states, most of whom are expected to be ‘dark’ states that are thus difficult to identify. So far, there has been no experimental test that has authoritatively confirmed or contradicted these predictions. The paper considers the response of the TDDFT-calculated excited states to applied electric fields of the order of those experienced by the chlorophylls in Photosystem-I (PS-I). TDDFT calculations using the PW91 density functional with the 6-31G* basis set are shown to predict that charge-transfer bands form the lowest excited state under these conditions, contrary to experimental results. In general, TDDFT calculations using modern functionals are shown to be unreliable for calculations of the excited states of chlorophylls, although important, realistic spectral information is depicted within them that may possibly be extracted for useful purposes. [ABSTRACT FROM AUTHOR]

The paper describes a density functional theory methodology using the B3LYP functional, with small correction terms introduced for open shell doublet states and closed-shell anions. The procedure is based on a B3LYP/6-31G(d) geometry optimization and frequency determination, followed by (RO)B3LYP/6-311?+?G(2d,2p) single point energy calculations. Using a correction term of +8.368?kJ?mol -1 for (doublet) radicals and?+?4.184?kJ?mol -1 for (closed shell) anions, close agreement is obtained with experiment (i.e. within 10?kJ?mol -1 ) for a series of molecular properties. These include bond dissociation enthalpies for X–H, where X?=?functional groups containing C, N, O, F, S, and X–Y, where X and Y are binary combinations of the same five heavy atoms plus Si and Cl, ionization potentials, electron and proton affinities, and gas-phase acidities. Using locally dense basis sets the approach can be extended to bond dissociation enthalpy calculations of large molecules with only a small increase in error. Using the same approach and popular solvation models allows a good starting point for reaction properties in solution. The approach is termed ’niversal' because by applying these corrections there is no need to change functionals and/or basis sets to obtain accurate results for different molecular properties, unlike some of the work reported previously. [ABSTRACT FROM AUTHOR]

In this paper, first principles were used to obtain a set of lateral interactions of oxygen atoms adsorbed on Pt (111) which can be applied in future studies of the phase diagram of O-Pt (111). Density functional theory (DFT) total energy computations were performed for fifteen configurations of oxygen adsorbed on Pt (111), with oxygen coverages ranging from zero to one. A cluster expansion was then carried out to fit lateral interaction parameters between and among oxygen atoms. The interaction parameters extracted from first principles indicate that strong repulsions exist between first (237.1 meV) and second nearest neighbours (39.5 meV), and weak attractions exist between third nearest neighbours (-5.8 meV). These weak attractions may explain the formation of islands of oxygen with p(2 × 2) symmetry, observed to form on Pt (111). [ABSTRACT FROM AUTHOR]

There are now many density functionals which are recommended for use in the literature. Most of them have been parametrized or designed with the calculation of energetic properties in mind. This paper looks at their predictions for magnetic properties, specifically magnetizabilities and nuclear shielding constants; the latter are one of the most useful predictions provided by computational chemistry. The results demonstrate that functionals do best for the properties for which they were optimized. It is therefore important to investigate the cause of errors in the calculated magnetic response properties bearing in mind that previous uncoupled DFT studies on nuclear shielding constants found them to be too deshielded and this was rationalized in terms of the known deficiency of existing functionals in underestimating the epsilon[sub a] - epsilon[sub i] energy differences, which in turn leads to an overestimation of the paramagnetic shielding terms. The work reported tests whether the improvement of the low lying and higher lying virtual orbitals and eigenvalues using the recently developed HCTH and asymptotically corrected HCTH(AC) functionals, respectively, produces improved predictions of the magnetizabilities and nuclear shielding constants with reference to the other GGA functionals LDA, BLYP and the hybrid functionals B97, B97-1, B3LYP and B3P86. In addition, these results are compared with Malkin's sum-over-states density functional perturbation theory (SOSDFPT) NMR shielding tensor calculations, where a level shift correction is applied to the DFT orbital energies leading to a substantial improvement in the shieldings. For the magnetizabilities, HCTH and HCTH(AC) give results inferior to BLYP, but the hybrid density functionals produce a significant improvement in the calculated DFT magnetizabilities (with an accuracy equivalent to MP2 level). For the nuclear shielding constants, HCTH and HCTH(AC) give the best results amongst all the DFT functionals, with an accuracy intermediate between the coupled-perturbed Hartree-Fock SCF and the reference MP2 values. This implies that DFT is not yet competitive with ab initio correlated calculations for these shielding constants. [ABSTRACT FROM AUTHOR]

This computational study characterises charge-transfer-to-solvent (CTTS) states of aqueous thiocyanate anion using equation-of-motion coupled-cluster methods combined with electrostatic embedding quantum mechanics/molecular mechanics (QM/MM) scheme. Equilibrium sampling was carried out using classical molecular dynamics (MD) with standard force-fields and QM/MM ab initio molecular dynamics (AIMD) using density functional theory. The two calculations yield significantly different local structure around solvated SCN − . Because of the diffuse character of CTTS states, they are very sensitive to the local structure of solvent around the solute and its dynamic fluctuations. Owing to this sensitivity, the spectra computed using MD and AIMD based snapshots differ considerably. This sensitivity suggests that the spectroscopy exploiting CTTS transitions can provide an experimental handle for assessing the quality of force-fields and density functionals. By combining CTTS-based spectroscopies with reliable theoretical modeling, detailed microscopic information of the solvent structure can be obtained. We present a robust computational protocol for modeling spectra of solvated anions and emphasise the use of an ab initio characterization of individual electronic transitions as CTTS or local excitations. [ABSTRACT FROM AUTHOR]

Comments on the calculation of molecular interactions by the differences of separate total energies. Inapplicable to Density Functional code in constructing the Kohn-Sham matrix; Unavailable supporting calculations for the justification of the idea on 'Function Counterpoise'; Unpublished subsequent paper showing an improvement in the binding energy.

A computational study of tris(2-phenylpyridine)iridium, Ir(ppy)3, is presented. The perspective is that of using organo-transition-metal complexes as phosphorescent species in light-emitting diodes (OLED's). Quantum yields approaching 100% are possible through a triplet harvesting mechanism. Complexes such as Ir(ppy)3 are amenable to exacting experimental and theoretical studies: small enough to accommodate rigor, yet large enough to support bulk phenomena in a range of host materials. The facial and meridional isomers differ by ∼220 meV, with fac-Ir(ppy)3 having the lower energy. Because fac-Ir(ppy)3 dominates in most environments, focus is on this species. Time-dependent density functional theory using long-range-corrected functionals (BNL and ωB97X) is used to calculate excited states of Ir(ppy)3 and a few low energy states of . The calculated T1 – S0 energy gap (2.30 eV) is in reasonable agreement with the experimental value of 2.44 eV. Only a few percent of singlet character in T1 is needed to explain so short a phosphorescence lifetime as 200 ns, because of the large and absorption cross-sections. Equilibrium geometries are calculated for S0, T1, and the lowest cation state (D0), and several ionization energies are obtained: adiabatic (5.86 eV); vertical from the S0 equilibrium geometry (5.88 eV); and vertical ionization of T1 at its equilibrium geometry (5.87 eV). These agree with a calculation by Hay (5.94 eV), and with the conservative experimental upper bound of 6.4 eV. Molecular orbitals provide qualitative explanations. A calculated UV absorption spectrum, in which transitions are vertical from the S0 equilibrium geometry, agrees with the room temperature experimental spectrum. This is consistent with Franck–Condon factors dominated by , as expected given the delocalized nature of the orbitals. Ir(ppy)3 vibrational frequencies were calculated and used to estimate the probability density for 500 K, i.e. the temperature at which the experiments were carried out. In combination with the vibrational energy imparted through photoexcitation, it is seen that a large amount of vibrational energy appears in without causing its fragmentation. Specifically, for  = 15,000 cm−1, the probability density for total vibrational energy peaks at ∼31,000 cm−1 with a 7800 cm−1 width. [ABSTRACT FROM AUTHOR]

Aspects of the science and the ways of doing science characteristic of the two senior scientists of Quantum Theory Project (QTP) in the period 1969-1985 are discussed from the perspective of the only QTP faculty member of that era who did not grow up in either the Lowdin or Slater schools. [ABSTRACT FROM AUTHOR]

As a first step towards a density functional theory (DFT) of wetting by ionic solutions we examine the density profiles of ions and solvent molecules confined near a charged wall, or between two walls, and the corresponding interfacial properties, including adsorption, surface tension, solvation force and electrostatic properties, within the semi-primitive model (SPM) of solutions made up of hard sphere solvent particles and charged hard spheres. Both monovalent and divalent cations with species-dependent diameters are considered. The density functional includes the best available Rosenfeld hard-sphere functional, as well as mean-field and Coulomb correlation contributions. The simpler mean-field functional is found to be adequate, at least for monovalent ions. The size differences lead to an interesting ‘fine structure’ of the density and charge density profiles. Cohesive interactions between all species are shown to lead to significant changes in the density profiles. [ABSTRACT FROM AUTHOR]

Various manifestations of structural crossover in the properties of a binary mixture of hard-spheres are studied. For homogeneous mixtures that are sufficiently asymmetric, there is a crossover line in the phase diagram such that for thermodynamic states that lie on one side, the decay of the three bulk pair correlation functions is oscillatory with a common wavelength approximately equal to the diameter of the smaller spheres, and for states on the other side, the common wavelength is approximately the diameter of the bigger spheres. Using density functional theory it is shown that structural crossover manifests itself in the intermediate range decay of (i) the one-body density profiles of a hard-sphere mixture adsorbed at planar walls, (ii) the effective (depletion) potential between two big hard-spheres immersed in the same binary mixture, and (iii) the solvation force, or excess pressure, of the same mixture confined between two planar hard walls. The structural crossover line is determined exactly for a one-dimensional binary mixture of hard-rods and evidence is presented, based on density functional theory calculations and Monte-Carlo simulations, for structural crossover in homogeneous binary mixtures of hard-disks in two dimensions. By considering a multicomponent mixture of hard-spheres, with an appropriate bimodal distribution of diameters, it is argued that structural crossover should still occur in the presence of polydispersity and that these results could be relevant to colloidal mixtures where correlation functions can be measured using real-space techniques. [ABSTRACT FROM AUTHOR]

This article focuses on the density functional theory (DFT) of researcher Nicholas Handy. To achieve reproducibility it is essential that these integrals be evaluated accurately, which requires high quality numerical integration. Handy and co-workers examined the reliability of quadrature schemes, presenting highly converged results and highlighting the efficiency of the Euler-Maclaurin radial integration scheme. The accuracy of a DFT calculation is governed by the exchange-correlation energy functional. From the outset, Handy and co-workers have attempted to understand and develop improved approximations to this quantity.

We have constructed transferable local atomic polarizability models for the n-alkanes by fitting them to the responses of the molecules to point charges at a large number of neighbouring points. By fitting simultaneously to a set of molecules, we have been able to obtain sets of transferable local polarizabilities and to demonstrate that they give a good account of the molecular polarizabilities. An important feature of our approach is that it can be used to determine atom-atom dispersion coefficients, including anisotropy. [ABSTRACT FROM AUTHOR]

Adsorption of water modelled by an extended primitive model (EPM5) and the underlying fluid of pseudo-hard bodies (PHBs) at a hard wall is studied by means of the density functional theory (DFT). Tarazona's weighted density approximation (also known as Mark II) is used, with a newly constructed weight function which yields the best possible match with the known pair direct correlation function of PHB. The weight function substantially differs from the weight function of hard spheres. In order to test the theory, a series of Monte Carlo simulations at various densities and temperatures is performed. It is clearly demonstrated that the new weight function leads to a significant improvement over the results based on the hard sphere weight function. It is also shown that unlike the simulations of a PHB fluid, the simulations of EPM5 at a hard wall at certain densities and temperatures are rather difficult to perform and density profiles are unreliable, in particular in the region where the crossover from adsorption to desorption takes place. [ABSTRACT FROM AUTHOR]

The depletion potentials between two infinite planes, and between two large spheres, due to polydisperse mixtures of non-interacting polymer coils and of interacting small hard spheres, are calculated over a wide range of polydispersities and of polymer or colloid concentrations. The case of non-interacting polymers can be treated analytically within a generalization of the Asakura-Oosawa model. The more difficult case of a polydisperse bath of hard spheres is treated within Rosenfield's 'fundamental measure' formulation of density functional theory. Polydispersity is found to have little effect on the depletion attraction, but to strongly reduce the repulsive barrier due to correlation and to damp the subsequent oscillations in the depletion potential. [ABSTRACT FROM AUTHOR]

With inspiration derived from recent discoveries of the tubular molecular rotor TaB20−, we performed the structural, electronic and spectral properties of a NbB20− cluster by using the CALYPSO searching method and density functional theory. The calculated results showed that a metal-centred tubular molecular rotor (Cs) with a B2 unit over the B18 drum is the global minimum. Photoelectron spectra are simulated by using the Multiwfn program, which is a powerful method to validate our obtained ground state structure. From the lowest energy structure, electronic and spectral properties are analysed, respectively, by calculating molecular orbitals, charge transfer, bond order, dipole moment and polarisability, the infrared spectra and Raman spectra. We hope that knowledge obtained from this study can be helpful for future theoretical and experimental syntheses of novel niobium-doped boron-based nanomaterials. [ABSTRACT FROM AUTHOR]

The article discusses the research conducted by Abhisek Ghosal and Amlan K. Roy on the optimization of range-separated hybrid (RSH) density functionals in molecular physics. The researchers propose a self-consistent systematic optimization method for RSH functionals from first principles. They demonstrate that their approach can improve the accuracy of property calculations, particularly those derived from frontier orbital energies. The research has practical implications in computational materials science and quantum chemistry, including the design of new materials and the calculation of charge-transfer excitation energies. The authors also discuss the future development of their research area, focusing on improving the performance of RSH functionals and integrating (G)KS-DFT with advanced many-body approaches. Abhisek Ghosal expresses gratitude for receiving the Molecular Physics Early Career Researcher Prize and acknowledges the support of his supervisor, Prof. Amlan K. Roy. [Extracted from the article]

Here are the author's reminiscences of his postdoctoral years in the SSMTG of Prof John C. Slater at MIT. [ABSTRACT FROM AUTHOR]

Molecular and electronic structures and UV-vis spectra of selected actinide(III) motexafins ([An-Motex]2+, An = Ac, Cm, Lr) as well as of uranyl(IV) motexafin ([UO2-Motex]+) were studied by using density functional theory methods combined with relativistic energy-consistent 5f-in-core actinide pseudopotentials. Solvent effects were considered by an explicit treatment of the first water coordination sphere in combination with the COSMO solvation model for bulk hydration effects. It is concluded that the Ac(III), Cm(III), Lr(III), and uranyl(IV) cations are tightly bound to the macrocyclic skeleton, yielding stable structures. By calculating the changes of the Gibbs free energies ΔG for the reactions X-Motex− + Y → X + Y-Motex− (X = La3+, Eu3+, Gd3+, Lu3+; Y = UO 2 2 + , Am3+, Cm3+), it is found that although in aqueous solution the Motex− ligand prefers Ln3+ (Ln = Eu, Gd, Lu) over An3+ (An = Am, Cm) it rather prefers UO 2 2 + over Ln3+ (Ln = La, Eu, Gd, Lu). The results suggest that motexafin might be useful for the separation of uranyl in nuclear waste treatments and possibly also for the treatment of uranyl poisoning in vivo. In particular motexafin might be a chelating agent for 225Ac3+ in targeted α-therapy. [ABSTRACT FROM AUTHOR]

The hybrid particle-field molecular dynamics method is an efficient alternative to standard particle-based coarse grained approaches. In this work, we propose an automated protocol for optimisation of the effective parameters that define the interaction energy density functional, based on Bayesian optimisation. The machine-learning protocol makes use of an arbitrary fitness function defined upon a set of observables of relevance, which are optimally matched by an iterative process. Employing phospholipid bilayers as test systems, we demonstrate that the parameters obtained through our protocol are able to reproduce reference data better than currently employed sets derived by Flory-Huggins models. The optimisation procedure is robust and yields physically sound values. Moreover, we show that the parameters are satisfactorily transferable among chemically analogous species. Our protocol is general, and does not require heuristic a posteriori rebalancing. Therefore it is particularly suited for optimisation of reliable hybrid particle-field potentials of complex chemical mixtures, and extends the applicability corresponding simulations to all those systems for which calibration of the density functionals may not be done via simple theoretical models. [ABSTRACT FROM AUTHOR]

The monomeric flavan-3-ols, namely (+) catechin (CT) and (−) epicatechin (ECT), are two important antioxidants available in nature. Density functional theory method has been used to study the homolytic, heterolytic bond cleavages and the associated radical scavenging activities at B3LYP/6-311G(2d,2p) level of theory. The radical scavenging mechanism of CT and ECT was studied by considering three scavenging mechanisms, namely hydrogen atom transfer (HAT), single-electron transfer-proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET). Parameters related to the above mechanisms, such as bond dissociation enthalpy (BDE), ionisation potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy in gas and solvent medium (benzene, methanol and water) were studied. The results suggest that 4'-OH site from B-ring would play a crucial role in the scavenging activity of both the compounds. We observed that HAT is a thermodynamically favoured mechanism in the gas phase, whereas SPLET mechanism is more preferential in the polar medium for both the compounds. The global descriptors, such as ionisation potential (IPv), electron affinity (EAv), chemical hardness (η), softness (S), electronegativity (χ) and electrophilic index (ω) also confirm the high antioxidant activity of CT and ECT. Reactive site of the electrophilic and nucleophilic attack is confirmed and visualised by molecular electrostatic potential (MEP) map. Highlights The optimised geometrical parameters of (+) catechin (CT) and (−) epicatechin (ECT) have been calculated using B3LYP with 6-311G(2d,2p) level of theory. The antioxidant properties of CT and ECT are compared using three mechanisms, namely hydrogen atom transfer (HAT), single-electron transfer-proton transfer (SET-PT), and sequential proton loss Electron transfer (SPLET) by homolytic and heterolytic bond cleavages. The hydroxyl group present at 4' site from B-ring is the most preferential site for hydrogen donation in both the compounds. The HAT mechanism is thermodynamically preferred in the gas phase, while SPLET mechanism is more favourable in polar solvents. Identification of reactive site by MEP and global descriptors is also confirming the high antioxidant activity in both compounds at the gas phase [ABSTRACT FROM AUTHOR]

A triphenylamine-based dye sensitizer–the electron donor, added with the embellishment, was designed and analyzed, to serve as a backup molecule for the sensitized solar cells (DSSCs). For a more realistic performance, five sensitizer molecules (ND, NDSH-1∼4) with triphenylamine (TPA) units as election donors (D), 4-benzo[c] [1, 2, 5] thiadiazol segment as acting as auxiliary acceptors (A), 4-ylethynyl as bridge (π) and benzoic acid as the electron acceptor (A) were explored in dichloromethane solvent by the methods of Density functional theory (DFT) and Time-dependent density functional theory (TD-DFT). Meanwhile, to understand the working process of DSSCs more systematically, these dyes adsorbed on (TiO2)16 were further explored. Finally, the effects of triphenylamine modification are summarized and disclosed from the phenomenon of simulation. The results show that the nitrogen-substituted hexyloxy dye exhibits a very narrow band gap and has a distinct red-shifted absorption band compared to the experimental dye ND. [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]

We perform all-electron, pure-sampling quantum Monte Carlo (QMC) calculations on ethylene and bifuran molecules. The orbitals used for importance sampling with a single Slater determinant are generated from Hartree-Fock and density functional theory (DFT). Their fixed-node energy provides an upper bound to the exact energy. The best performing density functionals for ethylene are BP86 and M06, which account for 99% of the electron correlation energy. Sampling from the π-electron distribution with these orbitals yields a quadrupole moment comparable to coupled cluster CCSD(T) calculations. However, these, and all other density functionals, fail to agree with CCSD(T) while sampling from electron density in the plane of the molecule. For bifuran, as well as ethylene, a correlation is seen between the fixed-node energy and deviance of the QMC quadrupole moment estimates from those calculated by DFT. This suggests that proximity of DFT and QMC densities correlates with the quality of the exchange nodes of the DFT wave function for both systems. [ABSTRACT FROM AUTHOR]

The magnetic and optical properties of Cu-doped ZnO systems have been widely studied in experimental, but the magnetic sources of the coexistence of Cu replacing Zn and the O vacancy systems are controversial. First-principles can compensate for the experimental deficiencies. The effects of Cu-doping and point defects on the magnetic and optical properties of ZnO were studied using geometry optimisation and energy calculation based on first-principle generalised gradient approximation + U method of the density functional theory. Results indicate that the band gaps and absorption spectra of Zn15CuO16, Zn14CuO16, and Zn15CuiO16 systems become narrowed and red-shifted, respectively, compared with those of pure ZnO. In addition, the system with Cu replaces Zn, and Zn vacancy coexists in ZnO. The doping system has the relatively largest magnetic moment and can achieve a ferromagnetic long-range order, and the Curie temperature can reach room temperature. As an electron injection source, this system can reach 100% electron spin-polarisation and exhibit half-metallic properties, which are relatively favourable for dilute magnetic semiconductor (DMS). Therefore, this system has certain theoretical reference value in the design and preparation of light-emitting devices or DMS. [ABSTRACT FROM AUTHOR]

The working equations for the calculation of mixed second- and third-order energy derivatives in the framework of auxiliary density functional theory are presented. The perturbations with respect to nuclear displacements and external homogeneous electric field components are calculated with auxiliary density perturbation theory. The presented energy derivative working equations were implemented in deMon2k and validated by vibrational spectra simulations within the double harmonic approximation. The effect of the auxiliary functions on the IR and Raman spectra simulation were analysed for the C60 fullerene. As applications, vibrational spectra of icosahedral carbon fullerenes with up to 540 atoms are calculated without employing symmetry constraints. [ABSTRACT FROM AUTHOR]

Hyper-generalised-gradient approximations (hGGAs) for the exact exchange-correlation functional are increasingly popular in density functional theory. HGGAs model nondynamical correlation using a flexible local combination of exact (Hartree–Fock, HF) exchange and approximate exchange. We present a simplified 'Rung 3.5' upper bound to the HF exchange energy density, the essential ingredient of hGGAs. We also present a nonempirical generalised gradient approximation for this upper bound. Both upper bounds go to zero in the high-density and density tail limits, facilitating the construction of hGGAs that recover HF exchange in these limits. The 'Rung 3.5' construction enables facile evaluation of analytic derivatives and calculations in periodic boundary conditions. Extensive numerical tests show that the upper bounds capture the critical difference between HF and approximate exchange, showing these ingredients' promise for building simple hGGAs. The tests also indicate a need for more sophisticated semi-local upper bounds. [ABSTRACT FROM AUTHOR]

Hot localised charge carriers on the Si(111)-7×7 surface are modelled by small charged clusters. Such resonances induce non-local desorption, i.e. more than 10 nm away from the injection site, of chlorobenzene in scanning tunnelling microscope experiments. We used such a cluster model to characterise resonance localisation and vibrational activation for positive and negative resonances recently. In this work, we investigate to which extent the model depends on details of the used cluster or quantum chemistry methods and try to identify the smallest possible cluster suitable for a description of the neutral surface and the ion resonances. Furthermore, a detailed analysis for different chemisorption orientations is performed. While some properties, as estimates of the resonance energy or absolute values for atomic changes, show such a dependency, the main findings are very robust with respect to changes in the model and/or the chemisorption geometry. [ABSTRACT FROM AUTHOR]

Benzene (C6H6) and polycyclic hydrocarbons such as naphthalene (C10H8), anthracene (C14H10) and coronene (C24H12) are well known aromatic organic compounds. We study the substitution of Li replacing all H-atoms in these hydrocarbons using density functional method. The vertical ionisation energy of such lithiated species, i.e. C6Li6, C10Li8, C14Li10 and C24Li12 ranges 4.24-4.50 eV, which is lower than the ionisation energy (IE) of Li atom. Thus, these species may behave as superalkalis due to their lower IE than alkali metal. However, these lithiated species possess planar and closed-shell structure, unlike typical superalkalis. Furthermore, all Li-substituted species are aromatic although their degree of aromaticity is reduced as compared to corresponding hydrocarbon analogues. We have further explored the structure of C6Li6 as star-like, unlike its inorganic analogue B3N3Li6, which appears as fan-like structure. We have also demonstrated that the interaction of C6Li6 with a superhalogen (such as BF4) is similar to that of a typical superalkali (such as OLi3). This may further suggest that the proposed lithiated species may form a new class of closed-shell organic superalkalis with aromaticity. [ABSTRACT FROM AUTHOR]

Electron affinity (EA) is the energy released when an additional electron is attached to an atom or a molecule. EA is a fundamental thermochemical property, and it is closely pertinent to other important properties such as electronegativity and hardness. However, accurate prediction of EA is difficult with density functional theory methods. The somewhat large error of the calculated EAs originates mainly from the intrinsic delocalisation error associated with the approximate exchange—correlation functional. In this work, we employ a previously developed non-empirical global scaling correction approach, which explicitly imposes the Perdew-Parr-Levy-Balduz condition to the approximate functional, and achieve a substantially improved accuracy for the calculated EAs. In our approach, the EA is given by the scaling corrected Kohn-Sham lowest unoccupied molecular orbital energy of the neutral molecule, without the need to carry out the self-consistent-field calculation for the anion. [ABSTRACT FROM AUTHOR]

The energy surfaces of the ground and low-lying excited states of ethylene are challenging tests of multi-reference electronic structure methods. A variety of multi-reference wavefunction theories have been applied to this problem and the ensuing photochemistry has been well studied. Density-functional methods, however, have been less successful. In this work, the ‘B13’ strong-correlation density functional is used to generate multi-reference orbitals for the computation of the three lowest-lying singlet states. We explore the states and energies as a function of torsion angle, and as a function of the pyramidalisation angle with respect to the twisted orthogonal structure. The former features an avoided crossing at the orthogonal structure; the latter a Csslice through a conical intersection. Both features are well reproduced by our B13 method. [ABSTRACT FROM PUBLISHER]

Ab initioand density functional calculations have been performed to elucidate the mechanism of CH radical insertion into methane. The results show that the reaction can be viewed to occur via two stages. On the first stage, the CH radical approaches methane without large structural changes to acquire proper positioning for the subsequent stage, where H-migration occurs from CH4to CH, along with a C–C bond formation. Where the first stage ends and the second begins, a tight transition state was located using the B3LYP/6-311G(d,p) and MP4(SDQ)/6-311++G(d,p) methods. Using a rigid rotor – harmonic oscillator approach within transition state theory, we show that at the MP5/6-311++G(d,p)//MP4(SDQ)/6-311++G(d,p) level the calculated rate constants are in a reasonably good agreement with experiment in a broad temperature range of 145–581 K. Even at low temperatures, the insertion reaction bottleneck is found about the location of the tight transition state, rather than at long separations between the CH and CH4reactants. In addition, high level CCSD(T)-F12/CBS calculations of the remainder of the C2H5potential energy surface predict the CH+CH4reaction to proceed via the initial insertion step to the ethyl radical which then can emit a hydrogen atom to form highly exothermic C2H4+H products. [ABSTRACT FROM PUBLISHER]

The planar electric double layer is modelled by an electrode, inner layer and diffuse layer whose constant permittivities differ. A point ion modified Poisson–Boltzmann analysis is made of the model with the ions in the diffuse layer having a distance of closest approach to the electrode, which is greater than the inner layer thickness and mimics the ion radius of a primitive model electrolyte. Comparisons are made with existing Monte Carlo simulations for uncharged and charged electrodes. For 1:1 and 2:1 electrolytes with a charged electrode, the modified Poisson–Boltzmann theory successfully predicts the singlet ion normalised density functions and the mean electrostatic potential. With the uncharged electrode, the neglect of ion size is more critical and the theoretical predictions are now poor at the higher concentrations. [ABSTRACT FROM PUBLISHER]

The geometrical structures, relative stabilities, HOMO–LUMO energy gaps, natural charges and magnetic moments of (n = 1–8) clusters have been investigated at the B3PW91 level. The results indicate that the most stable (n = 1–8) clusters adopt a planar structure for even n and a 3D structure for odd n, with the exception of . Note further that one impurity Pd atom can greatly enhance the stability of pure gold clusters compared with two impurity Pd atoms. By analysing the relative stabilities and HOMO–LUMO energy gaps, we conclude that the cluster has a greater chemical stability than the other clusters. Natural population analysis results show that the electronic distribution of two Pd atoms in (n = 1–8) clusters is the same, except for the cluster, and the electrons mostly locate on the d orbital. The total magnetic moments of (n = 1–8) clusters were also studied. They present clear odd–even oscillations and are mainly located on the Pd atoms derived from the contribution of the 4d state. [ABSTRACT FROM PUBLISHER]