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In recent years, a number of dynamical density functional theories (DDFTs) have been developed for describing the dynamics of the one-body density of both colloidal and atomic fluids. In the colloidal case, the particles are assumed to have stochastic equations of motion and theories exist for both the case when the particle motion is overdamped and also in the regime where inertial effects are relevant. In this paper, we extend the theory and explore the connections between the microscopic DDFT and the equations of motion from continuum fluid mechanics. In particular, starting from the Kramers equation, which governs the dynamics of the phase space probability distribution function for the system, we show that one may obtain an approximate DDFT that is a generalization of the Euler equation. This DDFT is capable of describing the dynamics of the fluid density profile down to the scale of the individual particles. As with previous DDFTs, the dynamical equations require as input the Helmholtz free energy functional from equilibrium density functional theory (DFT). For an equilibrium system, the theory predicts the same fluid one-body density profile as one would obtain from DFT. Making further approximations, we show that the theory may be used to obtain the mode coupling theory that is widely used for describing the transition from a liquid to a glassy state. [ABSTRACT FROM AUTHOR]

In this paper we present results of density functional theory calculations on the configurations, band structures, and optical properties of halides MCl (M=K,Ag) intercalated single-wall SiC nanotubes. The results show that the M–Cl distances perpendicular to the tube axis are slightly smaller than the ones parallel to the tube axis, which could be due to the axial strain of MCl. The electronic and optical properties of the resulting MCl@SiCNT composite are modified with respect to both the bulk halide and the empty nanotube. It is shown that AgCl affects the structures and properties of SiC nanotubes more significantly than KCl, and that the interaction between the nanotube and the encapsulated halide is stronger for narrower SiC nanotube. The AgCl encapsulation into SiCNTs results in band gap narrowing of AgCl@SiCNTs. [ABSTRACT FROM AUTHOR]

This paper describes the development of the B3LYP localized orbital correction model which improves the accuracy of the B3LYP thermochemical predictions for compounds containing transition metals. The development of this model employs a large data set containing 36 experimental atomic energies and 71 bond dissociation energies. B3LYP calculations were carried out on these systems with different basis sets. Based on an electronic structure analysis and physical arguments, we built a set of 10 parameters to correct atomic data and a set of 21 parameters to correct bond dissociation energies. Using the results from our biggest basis set, the model was shown to reduce the mean absolute deviation from 7.7 to 0.4 kcal/mol for the atomic data and from 5.3 to 1.7 kcal/mol for the bond dissociation energies. The model was also tested using a second basis set and was shown to give relatively accurate results too. The model was also able to predict an outlier in the experimental data that was further investigated with high level coupled-cluster calculations. [ABSTRACT FROM AUTHOR]

Polypyrrole is a conjugated polymer prototype of conducting polymers. The energetically preferred spatial conformation of n-pyrrole oligomers (n=1–24) in both the reduced and oxidized phases is obtained and analyzed in this paper within the hybrid density functional theory. Binding energies, gap energies, radius of gyration, end-to-end distance, and vibrational frequencies are reported as functions of oligomer length. Reduced n-pyrrole are bent chains for all sizes showing a dramatic departure from planarity. Vibrational spectra of n-pyrrole oligomers indicate the presence of two fairly size-insensitive frequency regions, which increase in intensity with increasing oligomer size. Several oxidation levels were analyzed for n-pyrrole through the distribution of the carbon-carbon bond orders and single/double bond lengths. It is shown that the oxidation level is directly related to the way positive charge localizes along the n-pyrrole oligomer chain. If charge/n<1/3, the oligomers are bent and charge is delocalized; if charge/n>=1/3, the oligomers are planar and charge notoriously localizes in n/charge regions along the backbone. Calculations with electronegative dopants show that charge localizes in the neighborhood of the dopant. It is demonstrated that one localized state in the gap between the highest occupied and lowest-unoccupied states appears for every +2e in the oxidation level. The band structure of infinite reduced polypyrrole gives a band gap energy in excellent agreement with experiment. The evolution of the band gap and the charge-localized band as a function of polypyrrole oxidation level is reported. [ABSTRACT FROM AUTHOR]

This paper investigates the reactivity of elemental carbon films deposited from the vapor phase with Fe and Ni substrates at room temperature. X-ray photoelectron spectroscopy (XPS) measurements are presented as a method for evaluating kinetic reaction data. Carbon films are deposited on different surface orientations representing geometries from a dense atom packing as in fcc (111) to an open surface structure as in fcc (100). During annealing experiments several reactions are observed (carbon subsurface diffusion, carbide formation, carbide decomposition, and graphite ordering). These reactions and the respective kinetic parameters are analyzed and quantified by XPS measurements performed while annealing at elevated temperatures (620–820 K). The resulting activation barriers for carbon subsurface diffusion are compared with calculated values using the density functional theory. The determined kinetic parameters are used to reproduce the thermal behavior of carbon films on nickel surfaces. [ABSTRACT FROM AUTHOR]

A new method called adaptive force matching (AFM) has been developed that is capable of producing high quality force fields for condensed phase simulations. This procedure involves the parametrization of force fields to reproduce ab initio forces obtained from condensed phase quantum-mechanics/molecular-mechanics (QM/MM) calculations. During the procedure, the MM part of the QM/MM is iteratively improved so as to approach ab initio quality. In this work, the AFM method has been tested to parametrize force fields for liquid water so that the resulting force fields reproduce forces calculated using the ab initio MP2 and the Kohn–Sham density functional theory with the Becke–Lee–Yang–Parr (BLYP) and Becke three-parameter LYP (B3LYP) exchange correlation functionals. The AFM force fields generated in this work are very simple to evaluate and are supported by most molecular dynamics (MD) codes. At the same time, the quality of the forces predicted by the AFM force fields rivals that of very expensive ab initio calculations and are found to successfully reproduce many experimental properties. The site-site radial distribution functions (RDFs) obtained from MD simulations using the force field generated from the BLYP functional through AFM compare favorably with the previously published RDFs from Car–Parrinello MD simulations with the same functional. Technical aspects of AFM such as the optimal QM cluster size, optimal basis set, and optimal QM method to be used with the AFM procedure are discussed in this paper. [ABSTRACT FROM AUTHOR]

We present a method to compute the Fermi function of the Hamiltonian for a system of independent fermions based on an exact decomposition of the grand-canonical potential. This scheme does not rely on the localization of the orbitals and is insensitive to ill-conditioned Hamiltonians. It lends itself naturally to linear scaling as soon as the sparsity of the system’s density matrix is exploited. By using a combination of polynomial expansion and Newton-like iterative techniques, an arbitrarily large number of terms can be employed in the expansion, overcoming some of the difficulties encountered in previous papers. Moreover, this hybrid approach allows us to obtain a very favorable scaling of the computational cost with increasing inverse temperature, which makes the method competitive with other Fermi operator expansion techniques. After performing an in-depth theoretical analysis of computational cost and accuracy, we test our approach on the density functional theory Hamiltonian for the metallic phase of the LiAl alloy. [ABSTRACT FROM AUTHOR]

In this paper, we solve quantum many-body problem by propagating ensembles of trajectories and guiding waves in physical space. We introduce the “effective potential” correction within the recently proposed time-dependent quantum Monte Carlo methodology to incorporate the nonlocal quantum correlation effects between the electrons. The associated correlation length is calculated by adaptive kernel density estimation over the walker distribution. The general formalism is developed and tested on one-dimensional helium atom in laser field of different intensities and carrier frequencies. Good agreement with exact results for the atomic ionization is obtained. [ABSTRACT FROM AUTHOR]

This paper supersedes previous theoretical approaches to conceptual DFT because it provides a unified and systematic approach to all of the commonly considered formulations of conceptual DFT, and even provides the essential mathematical framework for new formulations. Global, local, and nonlocal chemical reactivity indicators associated with the “closed-system representation” ([Nα,Nβ,να(r),νβ(r)]) of spin-polarized density functional theory (SP-DFT) are derived. The links between these indicators and the ones associated with the “open-system representation” ([μα,μβ,να(r),νβ(r)]) are derived, including the spin-resolved Berkowitz–Parr identity. The Legendre transform to the “density representation” ([ρα(r),ρβ(r)]) is performed, and the spin-resolved Harbola–Chattaraj–Cedillo–Parr identities linking the density representation to the closed-system and open-system representations are derived. Taken together, these results provide the framework for understanding chemical reactions from both the electron-following perspective (using either the closed-system or the open-system representation) and electron-preceding perspective (density representation). A powerful matrix-vector notation is developed; with this notation, identities in conceptual DFT become universal. Specifically, this notation allows the fundamental identities in conventional (spin-free) conceptual DFT, the [Nα,Nβ] representation, and the [N=Nα+Nβ,NS=Nα-Nβ] representation to be written in exactly the same forms. In cases where spin transfer and electron transfer are coupled (e.g., radical+molecule reactions), we believe that the [Nα,Nβ] representation may be more useful than the more common [N,NS] representation. [ABSTRACT FROM AUTHOR]

A recently developed analysis method [J. Chem. Phys. 127, 124106 (2007)] for NMR spin-spin coupling constants employing two-component (spin-orbit) relativistic density functional theory along with scalar relativistic natural localized molecular orbitals (NLMOs) and natural bond orbitals (NBOs) has been extended for analyzing NMR shielding tensors. Contributions from a field-dependent basis set (gauge-including atomic orbitals) have been included in the formalism. The spin-orbit NLMO/NBO nuclear magnetic shielding analysis has been applied to methane, plumbane, hydrogen iodide, tetracholoplatinate(II), and hexachloroplatinate(IV). [ABSTRACT FROM AUTHOR]

Finding the underlying mechanism from the statistical properties of an experimental two-state trajectory generated from dynamics in a complex on-off multisubstate kinetic scheme (KS) is the aim of many experiments. Since the data explicitly shows only transitions between substates of different states, information about the KS is lost, resulting in equivalence of KSs, i.e., the occurrence of different KSs that lead to the same data, in a statistical sense. In order to deal with this phenomenon, a canonical (unique) form of reduced dimensions (RD) is built from the data. RD forms are on-off networks with connections only between substates of different states, where the connections usually have nonexponential waiting time probability density functions. In this paper, we give a list of (about 50) relationships between properties of the data, the topology of reduced dimension forms, and features of KSs. Many of these relationships involve symmetries in RD forms, KSs, and the data and irreversible transitions in KSs. These relationships are useful both in theoretical analysis of on-off KSs and in the analysis of the data. [ABSTRACT FROM AUTHOR]

In this paper, double ionization energies (DIEs) of gas-phase atoms and molecules are calculated by energy difference method with density functional theory. To determine the best functional for double ionization energies, we first study 24 main group atoms in the second, third, and fourth periods. An approximation is used in which the electron density is first obtained from a density functional computation with the exchange-correlation potential Vxc known as statistical average of orbital potentials, after which the energy is computed from that density with 59 different exchange-correlation energy functionals Exc. For the 24 atoms, the two best Exc functional providing DIEs with average absolute deviation (AAD) of only 0.25 eV are the Perdew–Burke–Ernzerhof functional modified by Hammer et al. [Phys. Rev. B 59, 6413 (1999)] and one known as the Krieger–Chen–Iafrate–Savin functional modified by Krieger et al. (unpublished). Surprisingly, none of the 20 available hybrid functionals is among the top 15 functionals for the DIEs of the 24 atoms. A similar procedure is then applied to molecules, with opposite results: Only hybrid functionals are among the top 15 functionals for a selection of 29 molecules. The best Exc functional for the 29 molecules is found to be the Becke 1997 functional modified by Wilson et al. [J. Chem. Phys. 115, 9233 (2001)]. With that functional, the AAD from experiment for DIEs of 29 molecules is just under 0.5 eV. If the two suspected values for C2H2 and Fe(CO)5 are excluded, the AAD improves to 0.32 eV. Many other hybrid functionals perform almost as well. [ABSTRACT FROM AUTHOR]

Morphology control is important for practical applications of composite materials that consist of functional polymers and nanoparticles. Toward that end, block copolymers provide useful templates to arrange nanoparticles in the scaffold of self-organized polymer microdomains. This paper reports theoretical predictions for the distribution of nanoparticles in the lamellar structures of symmetric diblock copolymers on the basis of a polymer density functional theory (DFT) and the potential distribution theorem (PDT). The DFT predicts periodic spacing of lamellar structures in good agreement with molecular dynamics simulations. With the polymer structure from DFT as the input, the PDT is used to examine the effects of particle size, surface energy, polymer chain length, and compressibility on the distribution of nanoparticles in the limit of low particle density. It is found that the nanoparticle distribution depends not only on the particle size and surface energy but also on the local structure of the microdomain interface, polymer chain length, and compressibility. The theoretical predictions are compared well with experiments and simulations. [ABSTRACT FROM AUTHOR]

Hybrid functionals are responsible for much of the utility of modern Kohn-Sham density functional theory. When rigorously applied to solid-state metallic and small band gap systems, however, the slow decay of their nonlocal Hartree-Fock-type exchange makes hybrids computationally challenging and introduces unphysical effects. This can be remedied by using a range-separated hybrid which only keeps short-range nonlocal exchange, as in the functional of Heyd et al. [J. Chem. Phys. 118, 8207 (2003)]. On the other hand, many molecular properties require full long-range nonlocal exchange, which can also be included by means of a range-separated hybrid such as the recently introduced LC-ωPBE functional [O. A. Vydrov and G. E. Scuseria, J. Chem. Phys. 125, 234109 (2006)]. In this paper, we show that a three-range hybrid which mainly includes middle-range Hartree-Fock-type exchange and neglects long- and short-range Hartree-Fock-type exchange yields excellent accuracy for thermochemistry, barrier heights, and band gaps, emphasizing that the middle-range part of the 1/r potential seems crucial to accurately model these properties. [ABSTRACT FROM AUTHOR]

In Part I [R. E. Beckham and M. A. Bevan, J. Chem. Phys. 127, 164708 (2007)], results were presented for the sedimentation equilibrium of concentrated colloidal dispersions using confocal scanning laser microscopy experiments, Monte Carlo (MC) simulations, and a local density approximation perturbation theory. In this paper, we extended the modeling effort on those systems to include nonlocal density functional theory (DFT), which is capable of predicting the microstructure of the sediment at length scales comparable to the colloidal particle dimension. Specifically, we use a closure-based DFT formulation to predict interfacial colloidal sedimentation equilibrium density profiles. The colloid-colloid and colloid-surface interactions were modeled with DLVO screened electrostatic potentials using parameters taken directly from the experimental work. The DFT profiles were compared to the experimental and MC results from Part I. Good agreement was found for relatively dilute interfacial colloidal fluids, but agreement was less satisfactory as interfacial layering became more pronounced for conditions approaching the onset of interfacial crystallization. We also applied DFT in an inverse sense using the measured colloid density profile to extract the underlying colloid-surface potential; this can be thought of as a microscopic analog to the well-known procedure of using the macroscopic (coarse-grained) density profile to extract the osmotic equation of state. For the dilute interfacial fluid, the inverse DFT calculations reproduced the true colloid-surface potential to within 0.5kT at all elevations. [ABSTRACT FROM AUTHOR]

We present a synergetic experimental/theoretical study of hydrated hexafluorobenzene anions. Experimentally, we measured the anion photoelectron spectra of the anions, C6F6-(H2O)n (n=0–2). The spectra show broad peaks, which shift to successively higher electron binding energies with the addition of each water molecule to the hexafluorobenzene anion. Complementing these results, we also conducted density functional calculations which link adiabatic electron affinities to the optimized geometric structures of the negatively charged species and their neutral counterparts. Neutral hexafluorobenzene-water complexes are not thought to be hydrogen bonded. In the case of C6F6-(H2O)1, however, its water molecule was found to lie in the plane of the hexafluorobenzene anion, bound by two O–H...F ionic hydrogen bonds. Whereas in the case of C6F6-(H2O)2, both water molecules also lie in the plane of and are hydrogen bonded to the hexafluorobenzene anion but on opposite ends. This study and that of Schneider et al. [J. Chem. Phys. 127, 114311 (2007), preceding paper] are in agreement regarding the geometry of C6F6-(H2O)1. [ABSTRACT FROM AUTHOR]

This paper presents response theory based on a spin-restricted Kohn-Sham formalism for computation of time-dependent and time-independent nonlinear properties of molecules with a high spin ground state. The developed approach is capable to handle arbitrary perturbations and constitutes an efficient procedure for evaluation of electric, magnetic, and mixed properties. Apart from presenting the derivation of the proposed approach, we show results from illustrating calculations of static and dynamic hyperpolarizabilities of small Si(3n+1)H(6n+3) (n=0,1,2) clusters which mimic Si(111) surfaces with dangling bond defects. The results indicate that the first hyperpolarizability tensor components of Si(3n+1)H(6n+3) have an ordering compatible with the measurements of second harmonic generation in SiO2/Si(111) interfaces and, therefore, support the hypothesis that silicon surface defects with dangling bonds are responsible for this phenomenon. The results exhibit a strong dependence on the quality of basis set and exchange-correlation functional, showing that an appropriate set of diffuse functions is required for reliable predictions of the first hyperpolarizability of open-shell compounds. [ABSTRACT FROM AUTHOR]

The optical properties of nematic liquid crystals have been extensively exploited in the production of devices working in the visible range of the spectrum. These same properties can be employed to make devices that function in the near infrared as required for telecommunications applications. However, it is generally observed that the birefringence of liquid crystal mixtures decreases with increasing wavelength, making it important to identify new materials, optimized for use in the near infrared region. One route to high birefringence is to operate close to an absorption band edge, which in the present context implies choosing highly conjugated materials which are potentially colored and, thus, not suited to traditional display applications. In this paper we explore the usefulness of dye molecules as birefringence enhancers in mixtures with conventional nematic liquid crystals. The optical properties, in particular, the absorption edge, polarizability, and birefringence, of families of known dyes are calculated at optical (589 nm) and infrared (1550 nm) wavelengths, using electronic density functional theory. We demonstrate the expected correlation between the proximity of the absorption edge and the magnitude of the birefringence, and estimate the birefringence enhancement occurring when each dye is incorporated in a guest-host system. [ABSTRACT FROM AUTHOR]

This is the first paper in a series of four dealing with the adsorption site, electronic structure, and chemistry of small Au clusters, Aun (n=1–7), supported on stoichiometric, partially reduced, or partially hydroxylated rutile TiO2(110) surfaces. Analysis of the electronic structure reveals that the main contribution to the binding energy is the overlap between the highest occupied molecular orbitals of Au clusters and the Kohn-Sham orbitals localized on the bridging and the in-plane oxygen of the rutile TiO2(110) surface. The structure of adsorbed Aun differs from that in the gas phase mostly because the cluster wants to maximize this orbital overlap and to increase the number of Au–O bonds. For example, the equilibrium structures of Au5 and Au7 are planar in the gas phase, while the adsorbed Au5 has a distorted two-dimensional structure and the adsorbed Au7 is three-dimensional. The dissociation of an adsorbed cluster into two adsorbed fragments is endothermic, for all clusters, by at least 0.8 eV. This does not mean that the gas-phase clusters hitting the surface with kinetic energy greater than 0.8 eV will fragment. To place enough energy in the reaction coordinate for fragmentation, the impact kinetic energy needs to be substantially higher than 0.8 eV. We have also calculated the interaction energy between all pairs of Au clusters. These interactions are small except when a Au monomer is coadsorbed with a Aun with odd n. In this case the interaction energy is of the order of 0.7 eV and the two clusters interact through the support even when they are fairly far apart. This happens because the adsorption of a Aun cluster places electrons in the states of the bottom of the conduction band and these electrons help the Au monomer to bind to the five-coordinated Ti atoms on the surface. [ABSTRACT FROM AUTHOR]

The Green’s function for the master equation and the generalized master equation in path representation is an infinite sum over the length of path probability density functions (PDFs). In this paper, the properties of path PDFs are studied both qualitatively and quantitatively. The results are used in building efficient approximations for Green’s function in 1D, and are relevant in modeling and in data analysis. [ABSTRACT FROM AUTHOR]

In the exact theory, the ground state energy of an open system varies linearly when the electron number is changed between two adjacent integers. This linear dependence is not reproduced by common approximate density functionals. Deviation from linearity in this dependence has been suggested as a basis for the concept of many-electron self-interaction error (SIE). In this paper, we quantify many-electron SIE of a number of approximations by performing calculations on fractionally charged atoms. We demonstrate the direct relevance of these studies to such problems of common approximate functionals as instabilities of anions, spurious fractional charges on dissociated atoms, and poor description of charge transfer. Semilocal approximations have the largest many-electron SIE, which is only slightly reduced in typical global hybrids. In these approximations the energy versus fractional electron number curves upward, while in Hartree-Fock theory the energy curves downward. Perdew-Zunger self-interaction correction [Phys. Rev. B 23, 5048 (1981)] significantly reduces the many-electron SIE of semilocal functionals but impairs their accuracy for equilibrium properties. In contrast, a long-range corrected hybrid functional can be nearly many-electron SIE-free in many cases (for reasons we discuss) and at the same time performs remarkably well for many molecular properties. [ABSTRACT FROM AUTHOR]

Linear and nonlinear IR spectroscopic studies of nucleic acids can provide crucial information on solution conformations of DNA double helix and its complex with other molecules. Carrying out density functional theory calculations of A-, B-, and Z-form DNA’s, the authors obtained vibrational spectroscopic properties as well as coupling constants between different basis modes. The vibrational couplings that determine the extent of exciton delocalization are strongly dependent on DNA conformation mainly because the interlayer distance between two neighboring base pairs changes with respect to the DNA conformation. The Z-DNA has comparatively small interlayer vibrational coupling constants so that its vibrational spectrum depends little on the number of base pairs, whereas the A-DNA shows a notable dependency on the size. Furthermore, it is shown that a few distinctively different line shape changes in both IR and two-dimensional IR spectra as the DNA conformation changes from B to A or from B to Z can be used as marker bands and characteristic features distinguishing different DNA conformations. [ABSTRACT FROM AUTHOR]

An ab initio direct Ehrenfest dynamics method with time-dependent density functional theory is introduced and applied to collisions of 5 eV oxygen atoms and ions with graphite clusters. Collisions at three different sites are simulated. Kinetic energy transfer from the atomic oxygen to graphite local vibrations is observed and electron-nuclear coupling resulting in electronic excitation within the graphite surface as well as alteration of the atomic charge is first reported in this paper. The three oxygen species studied, O(3P), O-(2P), and O+(4S), deposit different amounts of energy to the surface, with the highest degree of damage to the π conjugation of the cluster produced by the atomic oxygen cation. Memory of the initial charge state is not lost as the atom approaches, in contrast to the usual assumption. [ABSTRACT FROM AUTHOR]

Density functional theory as proposed by Rosenfeld [Phys. Rev. Lett. 63, 980 (1989)] is used to study hard sphere mixture exposed by cylindrically symmetric external field. Exploiting the symmetry of the system, explicit formulas for the weighted densities are derived. The resulting density profiles are compared with new grand canonical Monte Carlo simulations. The comparison reveals very good agreement between the predicted and simulated results even at high densities and very narrow pores. Finally, simple algorithms for computing complete elliptic functions of the first and second kinds that occur in the derived formulae are presented to make the paper self-contained. [ABSTRACT FROM AUTHOR]

The common density functionals for the exchange-correlation energy make serious self-interaction errors in the molecular dissociation limit when real or spurious noninteger electron numbers N are found on the dissociation products. An “M-electron self-interaction-free” functional for positive integer M is one that produces a realistic linear variation of total energy with N in the range of M-1≤Na=M, and so can avoid these errors. This desideratum is a natural generalization to all M of the more familiar one of one-electron self-interaction freedom. The intent of this paper is not to advocate for any functional, but to understand what is required for a functional to be M-electron self-interaction-free and thus correct even for highly stretched bonds. The original Perdew-Zunger self-interaction correction (SIC) and our scaled-down variant of it are exactly one- and nearly two-electron self-interaction-free, but only the former is nearly so for atoms with M>2. Thus all these SIC’s produce an exact binding energy curve for H2+, and an accurate one for He2+, but only the unscaled Perdew-Zunger SIC produces an accurate one for Ne2+, where there are more than two electrons on each fragment Ne+0.5. We also discuss LiH+, which is relatively free from self-interaction errors. We suggest that the ability of the original and unscaled Perdew-Zunger SIC to be nearly M-electron self-interaction-free for atoms of all M stems in part from its formal resemblance to the Hartree-Fock theory, with which it shares a sum rule on the exchange-correlation hole of an open system. [ABSTRACT FROM AUTHOR]

The Raman spectra of a series of push-pull molecules containing probenzenoid or quinoid spacers which are substituted with 1,3-dithiol-2-ylidene as donor and dicyano-methylene or barbituric acid as acceptors have been analyzed. The experimental spectra have been assigned and interpreted according to density functional theory calculations. Correlations between the Raman spectra of the isolated spacers and of the substituted molecules have been done. Raman bands in the 1620–1560 cm-1 interval provide vibrational markers of the quinoid↔aromatic structural evolution. This finding is supported by a careful inspection of geometrical parameters, namely, bond length alteration data and particular bond distances. As a result, the peak positions and relative intensities of these Raman features can be used to evaluate the benzenoid character of the spacer as a function of the donor/acceptor substitution pattern. This paper shows that Raman spectroscopy is a powerful spectroscopic tool for the analysis of the conjugational properties (i.e., intramolecular donor→acceptor charge transfer) of new organic materials. [ABSTRACT FROM AUTHOR]

In previous work the authors have presented a highly accurate two-spinor fully relativistic solution of the two-center Coulomb problem utilizing the finite-element method (FEM) and furthermore developed a relativistic minimax two-spinor linear combination of atomic orbitals (LCAO). In the present paper the authors present Dirac-Fock-Slater (DFS-) density functional calculations for two-atomic molecules up to super heavy systems using the fully nonlinear minimax FEM and the minimax LCAO in its linearized approximation (linear approximation to relativistic minimax). The FEM gives highly accurate benchmark results for the DFS functional. Especially considering molecules with up to super heavy atoms such as UubO and Rg2, the authors found that LCAO fails to give the correct systematic trends. The accurate FEM results shed a new light on the quality of the DFS-density functional. [ABSTRACT FROM AUTHOR]

In this paper the authors further develop and apply the direct-mapping density functional theory to calculations of the atomization energies and ionization potentials. Single-particle orbitals are determined by solving the Kohn-Sham [Phys. Rev. A. 140, 1133 (1965)] equations with a local effective potential expressed in terms of the external potential. A two-parametric form of the effective potential for molecules is proposed and equations for optimization of the parameters are derived using the exchange-only approximation. Orbital-dependent correlation functional is derived from the second-order perturbation theory in its Mo\ller-Plesset-type zeroth-order approximation based on the Kohn-Sham orbitals and orbital energies. The total atomization energies and ionization potentials computed with the second-order perturbation theory were found to be in agreement with experimental values and benchmark results obtained with ab initio wave mechanics methods. [ABSTRACT FROM AUTHOR]

Most applications of time-dependent density-functional theory (TDDFT) use the adiabatic local-density approximation (ALDA) for the dynamical exchange-correlation potential Vxc(r,t). An exact (i.e., nonadiabatic) extension of the ground-state LDA into the dynamical regime leads to a Vxc(r,t) with a memory, which causes the electron dynamics to become dissipative. To illustrate and explain this nonadiabatic behavior, this paper studies the dynamics of two interacting electrons on a two-dimensional quantum strip of finite size, comparing TDDFT within and beyond the ALDA with numerical solutions of the two-electron time-dependent Schrödinger equation. It is shown explicitly how dissipation arises through multiple particle-hole excitations, and how the nonadiabatic extension of the ALDA fails for finite systems but becomes correct in the thermodynamic limit. [ABSTRACT FROM AUTHOR]

The ground state structure for the CCCCCl radical was computed by using symmetry-adapted cluster configuration-interaction (SAC-CI) theory along with density functional theory to overcome the differences raised in the recently published paper [Y. Sumiyoshi et al., Chem. Phys. Lett. 414, 82 (2005)] between the theory and the experiment. SAC-CI results clearly support the earlier experimental conclusion that the radical has the bent ground state structure corresponding to 2Π symmetry. Contrarily, probably due to spin contamination, mixing of a bent doublet ground state with the quartet components of a linear structure, coupled-cluster singles and doubles (CCSD) calculations were unable to provide reliable results. Results obtained using density functional theory also show that the radical has a bent structure. Some low-lying doublet excited states were also studied using the SAC-CI theory. The energy difference between the ground Π state and the nearby Σ state is around 0.2 eV. The excitation energy for the transition with the largest oscillator strength agrees with the strongest absorption peak. [ABSTRACT FROM AUTHOR]

The purpose of this short paper is to present an alternative fundamental measure theory (FMT) for hard sphere mixtures. Keeping the main features of the original Rosenfeld’s FMT [Phys. Rev. Lett. 63, 980 (1989)] and using the dimensional and the low-density limit conditions a new functional is derived incorporating Boublík’s multicomponent extension [Mol. Phys. 59, 371 (1986)] of highly accurate Kolafa’s equation of state for pure hard spheres. We test the theory for pure hard spheres and hard sphere mixtures near a planar hard wall and compare the results with the original Rosenfeld’s FMT and one of its modifications and with new very accurate simulation data. The test reveals an excellent agreement between the results based on the alternative FMT and simulation data for density profile near a contact and some improvement over the original Rosenfeld’s FMT and its modification at the contact region. [ABSTRACT FROM AUTHOR]

Conformational disorder of conjugated polymers is an important issue to be understood and quantified. In this paper we present a new method to assess the chain conformation of conjugated polymers based on measurements of intrachain energy transfer. The chain conformation is modeled on the basis of monomer-monomer interactions, such as torsion, bending, and stretching of the connecting bond. The latter two potentials are assumed to be harmonic, while the torsional potential was calculated by density functional theory using B3-LYP functional with the SVP basis set. The energy transfer dynamics of excitons on these chains are quantitatively simulated using Förster-type line-dipole energy transfer. This allows us to compare the simulated ground state conformation of single polymer chains to ultrafast depolarization experiments of poly [3-(2,5-dioctylphenyl)thiophene] in solution. We identify torsional rotation as the main contributor to conformational disorder and find that this disorder is mainly controlled by the energy difference between syn and anti bonds. [ABSTRACT FROM AUTHOR]

Structural properties of liquid water at ambient temperature were studied using Car-Parrinello [Phys. Rev. Lett. 55, 2471 (1985)] ab initio molecular dynamics (CPAIMD) simulations combined with the Kohn-Sham (KS) density functional theory and the BLYP exchange-correlation functional for the electronic structure. Unlike other recent work on the same subject, where plane-wave (PW) or hybrid Gaussian/plane-wave basis sets were employed, in the present paper, a discrete variable representation (DVR) basis set is used to expand the KS orbitals, so that with the real-space grid adapted in the present work, the properties of liquid water could be obtained very near the complete basis set limit. Structural properties of liquid water were extracted from a 30 ps CPAIMD-BLYP/DVR trajectory at 300 K. The radial distribution functions (RDFs), spatial distribution functions, and hydrogen bond geometry obtained from the CPAIMD-BLYP/DVR simulation are generally in good agreement with the most up to date experimental measurements. Compared to recent ab initio MD simulations based on PW basis sets, less significant overstructuring was found in the RDFs and the distributions of hydrogen bond angles, suggesting that previous plane-wave and Gaussian basis set calculations have exaggerated the tendency toward overstructuring. [ABSTRACT FROM AUTHOR]

The accurate first principles description of the correlations between electrons has been a topic of interest in molecular physics. We have reported in our previous paper [J. Chem. Phys. 123, 144112 (2005)] that the T matrix, which is the ladder diagrams up to the infinite order, can accurately represent the short-range electron correlations while calculating the double ionization energy spectra of atoms and molecules. In this paper, we calculate the two-electron distribution functions of real systems (Ar, CO, CO2, and C2H2) from the eigenvalue equation associated with the Bethe-Salpeter equation for the T matrix by beginning with the local density approximation of the density functional theory and the GW approximation. We found that when the interelectron distance is very small, the Coulomb hole appears between antiparallel spin electrons due to the short-range repulsive Coulomb interaction. The resulting two-electron distribution functions clearly show the Coulomb hole. [ABSTRACT FROM AUTHOR]

We propose a general method of thermodynamic integration to find the free energy of a surface, where our integration parameter is taken to be the strain on the unit cell of the system (which in the example presented in this paper is simply the extension of the unit cell along the normal to the surface), and the integration is performed over the thermal average stress from a molecular dynamics run. In order to open up a vacuum gap in a continuous and reversible manner, an additional control interaction has been introduced. We also use temperature integration to find a linear relation for the temperature dependence of the free surface energy. These methods have been applied to the titanium dioxide (110) surface, using first principles density functional theory. A proof of principle calculation for zero temperature shows excellent agreement between the integral calculation and the difference in energy calculated by the DFT program. Calculations that have been performed at 295 and 1000 K give excellent agreement between the two integration methods. [ABSTRACT FROM AUTHOR]

In this paper, the second and third order polarizabilities of small GanAsm (n+m=4–10) clusters are systematically investigated using the time dependent density functional theory (TDDFT)/6-311+G* combined with the sum-over-states method (SOS//TDDFT/6-311+G*). For the static second order polarizabilities, the two-level term (βvec.2) makes a significant contribution to the βvec for all considered GanAsm clusters except for the Ga3As4 cluster. And, for the static third order polarizabilities, the positive channel (<γ>II) makes a larger contribution to 〈γ〉tot than the negative channel (<γ>I). Similar to the cubic GaAs bulk materials, the small GanAsm cluster assembled materials exhibit large second order (1×10-6 esu) and third order susceptibilities (5×10-11 esu). The dynamic behavior of β(-2ω;ω,ω) and γ(-3ω;ω,ω,ω) show that the small GanAsm cluster will be a good candidate of nonlinear optical materials due to the avoidance of linear resonance photoabsorption. [ABSTRACT FROM AUTHOR]

Semilocal density functional approximations (DFAs) for the exchange-correlation energy suffer from self-interaction error, which is believed to be the cause of many of the failures of common DFAs, such as poor description of charge transfer and transition states of chemical reactions. The standard self-interaction correction (SIC) of Perdew and Zunger mends some of these failures but spoils such essential properties as thermochemistry and equilibrium bond lengths. The Perdew-Zunger SIC seems to overcorrect many-electron systems. In this paper, we propose a modified SIC, which is scaled down in many-electron regions. The new SIC has an improved performance for many molecular properties, including total energies, atomization energies, barrier heights of chemical reactions, ionization potentials, electron affinities, and bond lengths. The local spin-density approximation (LSDA) benefits from SIC more than higher-level functionals do. The scaled-down SIC has only one adjustable parameter. Rationalization of the optimal value of this parameter enables us to construct an almost-nonempirical version of the scaled-down SIC-LSDA, which is significantly better than uncorrected LSDA and even better than the uncorrected generalized gradient approximation. We present an analysis of the formal properties of the scaled-down SIC and define possible directions for further improvements. In particular, we find that exactness for all one-electron densities does not guarantee correct asymptotics for the exchange-correlation potential of a many-electron system. [ABSTRACT FROM AUTHOR]

In this paper we present the theory and implementation of analytic derivatives of time-dependent density functional theory (TDDFT) excited states energies, both in vacuo and including solvent effects by means of the polarizable continuum model. The method is applied to two case studies: p-nitroaniline and 4-(dimethyl)aminobenzonitrile. For both molecules PCM-TDDFT is shown to be successful in supporting the analysis of experimental data with useful insights for a better understanding of photophysical and photochemical pathways in solution. [ABSTRACT FROM AUTHOR]

Given a general, N-particle Hamiltonian operator, analogs of the Hohenberg-Kohn theorem are derived for functions that are more general than the particle density, including density matrices and the diagonal elements thereof. The generalization of Lieb’s Legendre transform ansatz to the generalized Hohenberg-Kohn functional not only solves the υ-representability problem for these entities, but, more importantly, also solves the N-representability problem. Restricting the range of operators explored by the Legendre transform leads to a lower bound on the true functional. If all the operators of interest are incorporated in the restricted maximization, however, the variational principle dictates that exact results are obtained for the systems of interest. This might have important implications for practical work not only for density matrices but also for density functionals. A follow-up paper will present a useful alternative approach to the v- and N-representability problems based on the constrained search formalism. [ABSTRACT FROM AUTHOR]

In this paper we apply the direct-mapping density-functional theory (DFT) to open-shell systems, in order to get many-electron wave functions having the same transformation properties as the eigenstates of the exact Hamiltonians. Such a case is that of spin, where in order to get the magnetic properties, the many-particle states must be eigenstates not only of Sz but also of S2. In this theory the Kohn and Sham [Phys. Rev. A 140, 1133 (1965)] potential is expressed directly as a mapping of the external potential. The total energies of the molecules calculated were satisfactory as their relative deviations (ΔE/E) from the exact Hartree-Fock ones were of the order of 10-4. This accuracy is much higher than that of the standard DFT in its local exchange potential approximation. This method does not need an approximate density as input, as the effective potential is derived directly from the external potential. [ABSTRACT FROM AUTHOR]

In this paper the structures of 4-aminophenol(H2O)1+ and 3-aminophenol(H2O)1+ clusters are investigated in molecular beam experiments by different IR/UV-double resonance techniques as well as the mass analyzed threshold ionization spectroscopy yielding both inter- and intramolecular vibrations of the ionic and neutral species. Possible structures are extensively calculated at the level of density functional theory (DFT) or at the ab initio level of theory. From the experimental and theoretical investigations it can be concluded that in the case of 4-aminophenol(H2O)1 one O[Single_Bond]H...O hydrogen-bonded structure exists in the neutral cluster but two structures containing either an O[Single_Bond]H...O or a N[Single_Bond]H...O hydrogen-bonded arrangement are observed in the spectra of the ionic species. This observation is a result of an intramolecular rearrangement reaction within the ion which can only take place if high excess energies are used. A reaction path via the CH bonds is calculated and explains the experimental observations. In the case of 3-aminophenol(H2O)1+ only one O[Single_Bond]H...O bound structure is observed both in the neutral and ionic species. Ab initio and DFT calculations show that due to geometrical and energetical reasons a rearrangement cannot be observed in the 3-aminophenol(H2O)1+ cluster ion. [ABSTRACT FROM AUTHOR]

Based upon the optimized effective potential with the self-interaction correction, we present in this paper an alternative gradient-corrected density-functional approximation with the proper long-range behavior of the effective potential. As applied to the study of the interconfigurational energies of the whole transition-metal atoms, the present combination of the gradient-corrected contribution and the modified optimized effective potential lead the s ionization to the excellent agreement with the experiment. The calculated d ionizations and s–d transition energies are also discussed. [ABSTRACT FROM AUTHOR]

Previous work testing density functionals for use in calculating high-spin–low-spin energy differences, ΔEHL, for iron(II) spin-crossover transitions has tended to conclude that only properly reparametrized hybrid functionals can predict ΔEHL since it seems to depend critically on a correct description of the electron pairing energy governed by the exchange term. Exceptions to this rule are the previous three papers (I, II, and III in the present series of papers) where it was found that modern generalized gradient approximations (GGAs) and meta-GGAs could do as well as hybrid functionals, if not better, for this type of problem. In the present paper, we extend these previous studies to five more molecules which are too large to treat with high-quality ab initio calculations, namely, the series [Fe(L)(‘NHS4’)], where NHS4=2.2′-bis(2-mercaptophenylthio)diethylamine dianion, and L=NH3, N2H4, PMe3, CO, and NO+. Since we know of no reliable experimental estimate of ΔEHL, we content ourselves with a comparison against the experimentally determined ground-state spin symmetry including, in so far as possible, finite-temperature effects. Together with the results of Papers I, II, and III, this paper provides a test of a large number of functionals against the high-spin/low-spin properties of a diverse set of Fe(II) compounds, making it possible to draw some particulary interesting conclusions. Trends among different classes of functionals are discussed and it is pointed out that there is at least one functional, namely, the OLYP generalized gradient approximation, which is able to give a reasonably good description of the delicate spin energetics of Fe(II) coordination compounds without resorting to hybrid functionals which require the relatively more expensive calculation of a Hartree–Fock-type exchange term. [ABSTRACT FROM AUTHOR]

We propose a simulation method for infinitely dilute polymer solutions. In this method, an effective Hamiltonian of the solvated polymer chain is introduced to eliminate the degree of freedom of the solvent particle. The effective Hamiltonian is coupled with the density-functional theory (DFT) that we have developed for a polymer-solvent pair correlation function. All the equations proposed in this paper are derived from the first principle. This simulation method was applied to polymer chains in supercritical solvents. We observed anomalous behaviors of polymer chains near the liquid-vapor critical point: both solvophilic and solvophobic polymers expand significantly near the critical point; this is in contrast to the behavior of polymer chains in vacuum. This expansion can be interpreted as a cooperative phenomenon, which enhances the large long-wavelength density fluctuation of the solvent. [ABSTRACT FROM AUTHOR]

Orbital-free density-functional theory (OF-DFT) with modern kinetic-energy density functionals (KEDFs) is a linear scaling technique that accurately describes nearly-free-electron-like (main group) metals. In an attempt towards extending OF-DFT to transition metals, here we consider whether OF-DFT can be used effectively to study Ag, a metal with a localized d shell. OF-DFT has two approximations: use of a KEDF and local pseudopotentials (LPSs). This paper reports construction of a reasonably accurate LPS for Ag by means of inversion of the Kohn–Sham (KS) DFT equations in a bulk crystal environment. The accuracy of this LPS is determined within KS-DFT (where the exact noninteracting kinetic energy is employed) by comparing its predictions of bulk properties to those obtained from a conventional (orbital-based) nonlocal pseudopotential (NLPS). We find that the static bulk properties of fcc and hcp Ag predicted within KS-DFT using this LPS compare fairly well to those predicted by an NLPS. With the transferability of the LPS established, we then use this LPS in OF-DFT, where several approximate KEDFs were tested. We find that a combination of the Thomas–Fermi (TTF) and von Weizsäcker (TvW) functionals (TvW+0.4TTF) produces better densities than those from the linear-response-based Wang–Teter KEDF. However, the equations of state obtained from both KEDFs in OF-DFT contain unacceptably large errors. The lack of accurate KEDFs remains the final barrier to extending OF-DFT to treat transition metals. [ABSTRACT FROM AUTHOR]

Using the fluctuation-dissipation theorem (FDT) in the context of density-functional theory (DFT), one can derive an exact expression for the ground-state correlation energy in terms of the frequency-dependent density response function. When combined with time-dependent density-functional theory, a new class of density functionals results that use approximations to the exchange-correlation kernel fxc as input. This FDT-DFT scheme holds promise to solve two of the most distressing problems of conventional Kohn–Sham DFT: (i) It leads to correlation energy functionals compatible with exact exchange, and (ii) it naturally includes dispersion. The price is a moderately expensive O(N6) scaling of computational cost and a slower basis set convergence. These general features of FDT-DFT have all been recognized previously. In this paper, we present the first benchmark results for a set of molecules using FDT-DFT beyond the random-phase approximation (RPA)—that is, the first such results with fxc≠0. We show that kernels derived from the adiabatic local-density approximation and other semilocal functionals suffer from an “ultraviolet catastrophe,” producing a pair density that diverges at small interparticle distance. Nevertheless, dispersion interactions can be treated accurately if hybrid functionals are employed, as is demonstrated for He2 and HeNe. We outline constraints that future approximations to fxc should satisfy and discuss the prospects of FDT-DFT. [ABSTRACT FROM AUTHOR]

A recently developed density functional theory (DFT) for tethered bead-spring chains is used to investigate colloidal forces for the good solvent case. A planar surface of tethered chains is opposed to a bare, hard wall and the force exerted on the bare wall is calculated by way of the contact density. Previously, the case of large wall separation was investigated. The density profiles of the unperturbed chains, in that case, were found to be neither stepfunctions nor parabolas and were shown to accurately predict computer simulation results. In the present paper, the surface forces that result from the distortion of these density profiles at finite wall separation is studied. The resulting force function is analyzed for varying surface coverages, wall separations, and chain lengths. The results are found to be in near quantitative agreement with the scaling predictions of Alexander [S. Alexander, J. Phys. (Paris) 38, 983 (1977)] when the layer thickness is “correctly” defined. Finally, a hybrid Alexander–DFT theory is suggested for the analysis of experimental results. [ABSTRACT FROM AUTHOR]

This paper describes a systematic study on the clathrate structure of H+(H2O)21 using tandem mass spectrometry, vibrational predissociation spectroscopy, Monte Carlo simulations, and density functional theory calculations. We produced H+(H2O)n from a continuous corona-discharged supersonic expansion and observed three anomalies simultaneously at the cluster temperature near 150 K, including (1) the peak at n=21 is more intense than its neighboring ions in the mass spectrum, (2) the size-dependent dissociation fractions show a distinct drop for the 21-mer, and (3) the infrared spectrum of H+(H2O)21 exhibits only a single feature at 3699 cm-1, corresponding to the free-OH stretching of three-coordinated water molecules. Interestingly, the anomalies appear or disappear together with cluster temperature, indicating close correlation of these three observations. The observations, together with Monte Carlo simulations and density functional theory calculations, corroborate the notion for the formation of a distorted pentagonal dodecahedral (512) cage with a H2O molecule in the cage and a H3O+ ion on the surface for this “magic number” water cluster ion. The dodecahedral cage melts at higher temperatures, as evidenced by the emergence of a free-OH stretching feature at 3717 cm-1 for the two-coordinated water in H+(H2O)21 produced in a warmer molecular beam. Extension of this study to larger clusters strongly suggests that the experimentally observed isomer of H+(H2O)28 is most likely to consist of a distorted protonated pentakaidecahedral (51263) cage enclosing two neutral water molecules. [ABSTRACT FROM AUTHOR]

The midinfrared (MIR) spectra of molecules in polar solvents exhibit inhomogeneously broadened bands whose spectral positions are shifted as compared to the gas phase. The shifts are caused by interactions with structured solvation shells and the broadenings by fluctuations of these interactions. The MIR spectra can be calculated from hybrid molecular dynamics (MD) simulations, which treat the solute molecule by density functional theory and the solvent by molecular mechanics by the so-called instantaneous normal mode analysis (INMA) or by Fourier transforming the time correlation function (FTTCF) of the molecular dipole moment. In Paper I of this work [M. Schmitz and P. Tavan, J. Chem. Phys. 121, 12233 (2004)] we explored an alternative method based on generalized virial (GV) frequencies noting, however, that GV systematically underestimates frequencies. As shown by us these artifacts are caused by solvent-induced fluctuations of the (i) equilibrium geometry, (ii) force constants, and (iii) normal mode directions as well as by (iv) diagonal and (v) off-diagonal anharmonicities. Here we now show, by analyzing the time scales of fluctuations and sample MD trajectories of formaldehyde in the gas phase and in water, that all these sources of computational artifacts can be made visible by a Fourier analysis of the normal coordinates. Correspondingly, the error sources (i) and (iii)–(v) can be removed by bandpass filtering, as long as the spectral signatures of the respective effects are well separated from the fundamental band. Furthermore, the artifacts arising from effect (ii) can be strongly diminished by a time-resolved version of the GV approach (TF-GV). The TF-GV method then yields for each mode j a trajectory of the vibrational frequency ωj(t|τ) at a time resolution τ>τj, which is only limited by the corresponding oscillation time τj=2π/ωj and, thus, is in the femtosecond range. A correlation analysis of these trajectories clearly separates the librational motions from the conformational dynamics of the solvation shells and yields the inhomogeneously broadened MIR spectra, if the theory of motional narrowing is properly included. The MIR spectrum of formaldehyde in solution obtained by TF-GV agrees very well with the FTTCF result, if one applies the so-called “harmonic approximation” quantum correction factor and a temperature scaling to the FTTCF intensities. Also for INMA an excellent agreement is achieved if one disregards a slight INMA overestimate of linewidths.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recently an inorganic fullerine-like [As@Ni12@As20]3- onion with near-perfect icosahedral symmetry in the crystalline phase was reported [M. J. Moses, J. C. Fettinger, and B. W. Eichhorn, Science 300, 778 (2003)]. This paper presents a detailed computational study in the framework of density functional theory on various aspects of this molecule. The electronic structure of the As@Ni12@As20 is investigated in its neutral as well as -3 charged state together with its subunits As20 and As@Ni12 by the all electron linear combination of Gaussian-type orbitals method. The bonding is studied by examining the integrated charge within atomic sphere, the electron localization function, changes in the electron density distribution, and from vibrational modes. We find that strong covalent As-As bonds seen in isolated As20 become weaker in the As@Ni12@As20 and strong covalent As-Ni bonds are formed. The structural stability of all four clusters is examined by analyzing the energetics and by calculating the vibrational frequencies. Further, the infrared and Raman spectra is predicted for both the neutral and charged As@Ni12@As20 clusters. Finally, the energy barrier for removal of a single arsenic atom is calculated for the neutral As@Ni12@As20 cluster. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]