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We have employed density functional theory to study gas–liquid nucleation in binary fluids. Effects of surface enrichment and curvature are naturally included in this novel statistical mechanical approach, allowing the classical capillarity approximation to be tested. In this paper we apply the theory to mixtures of Lennard-Jones fluids (modeled on argon and krypton). For these nearly ideal mixtures, the magnitude of nonclassical effects tend to be small, but systematic deviations do appear, with the ratio of the classical to nonclassical rate showing a maximum at intermediate compositions. [ABSTRACT FROM AUTHOR]

Density functional theory is used to investigate two of the possible reasons for the discrepancy between theory and experiment for the interfacial width and tension of phase separated binary blends. The two reasons are the inadequacy of the density functionals used previously and the neglect of the composition dependence of the Flory interaction parameter χ. For the sake of algebraic simplicity, our computations are restricted to symmetric, incompressible binary blends with correlation functions taken in the random phase approximation. We extend the analysis in Paper I [Tang and Freed, J. Chem. Phys. 94, 1572 (1991)] on the validy of density functionals for binary blends to the strong segregation limit with narrow interfaces by studying the conditions under which the Roe free energy functional is appropriate. Our derivation in this limit resums a rigorous Landau expansion to show that the Roe functional is appropriate only for infinite molecular weights. Nevertheless, even in the strong segregation limit this functional becomes incorrect in the wings of the concentration profile where a Landau expansion is valid despite the current unavailability of a local density functional.Interfacial properties in the theoretically simplest weak segregation limit are in accord with those of previous workers, but we are able to suggest an interpolation form for the interfacial width and tension of symmetric blends that crosses over between the weak and strong segregation limits. The composition dependence of the Flory interaction parameter χ poses several problems when experimental χeff are substituted into theories that ignore this composition dependence. We therefore investigate the errors incurred by the use of different experimental measures of χ and by the use of χ measured at different compositions for two simple models in which χ varies linearly or quadratically with blend composition. Situations arise where there exists an experimental... [ABSTRACT FROM AUTHOR]

This paper is an extension of our previous work on density functional models of electrons in magnetic fields. A full ‘‘classical path’’ (CP) one-body Green’s function is used in the calculation of the kinetic functional and the one particle density. This treatment leads to a more precise expression of the density functional theory in the strong B case, in which magnetic fields are much stronger than the external scalar potential. In the semiclassical limit t→0, the CP Green’s function is checked by an exact solvable system, interactionless electrons in a central harmonic potential and a constant magnetic field. It turns out that the Green’s function is correct through the order O(t2). Furthermore, in the high B limit (but still t→0), the leading terms in B of the CP Green’s function are the same as those of the exact Green’s function in the entire t-expansion series. [ABSTRACT FROM AUTHOR]

A formally exact nonlocal density-functional expansion procedure for direct correlation functions developed earlier by Stell for a homogeneous system, and extended by Blum and Stell, Sullivan and Stell, and ourselves to various inhomogeneous systems, is used here to derive nonlocal integral-equation approximations. Two of the simplest of these approximations (zeroth order), which we shall characterize here as the hydrostatic Percus–Yevick (HPY) approximation and the hydrostatic hypernetted-chain (HHNC) approximation, respectively, are shown to be capable of accounting for wetting transitions on the basis of general theoretical considerations. Before turning to such transitions, we investigate in this first paper of a series the case of homogeneous hard-sphere fluids and hard spheres near a hard wall as well as the case of hard spheres inside a slit pore. Numerical results show that the HHNC approximation is better than the HNC approximation for both the homogeneous and inhomogeneous systems considered here while the HPY approximation appears to overcorrect the PY approximation. [ABSTRACT FROM AUTHOR]

We report the details of a theory which predicts the freezing of quantum liquids, such as helium [J. Chem. Phys. 90, 4622 (1989)]. The freezing of a wide variety of classical liquids has been described by the density functional (DF) theory of statistical mechanics. By choosing a new ideal system, we construct a new DF theory which addresses directly many of the unusual features of the freezing of liquid helium, such as the weakly modulated liquid pair correlation function g(r) at freezing densities. The theory combines DF techniques with the Feynman path integral formulation of quantum mechanics, to include correctly dispersion effects. In classical DF theories, the density and external field of the ideal system are connected by a Boltzmann relation ρ(r)∝exp[-βV(r)]. In our quantum DF theory, we relate the density and external field of the ideal system through the Feynman path integral representation, in which the quantum particle is represented by a classical ‘‘ring polymer’’ of P beads. In practical applications, the DF perturbation expansion is truncated at second order, and classical DF theories fail for helium because they employ an ideal system which is too far removed from the interacting system. For a certain simplified problem, the density path integral of the ideal system can be performed in closed form, leading to a compact, physically descriptive theory. In a companion paper, the full theory is applied to the freezing of helium-4 and yields good results. [ABSTRACT FROM AUTHOR]

The concept of local pressure in an electronic system is extended and developed, starting from an integral relation of Bartolotti and Parr (Ref. 11) and using the local thermodynamic language of Ghosh, Berkowitz, and Parr (GBP) (Ref. 3), who have shown that for an ideal, noninteracting microscopic system the internal pressure at a point r is purely kinetic and given by ps=ρ(r)kT(r), where T(r) is an appropriately defined local temperature. In the present paper, we show that this equation, exact for the noninteracting, ideal system within the local thermodynamic transcription is a first order truncation of the real, interacting system pressure density functional, which contains explicit correlation and exchange pressure contributions, which act as ‘‘deviations from ideality’’ in the real system. From analogy with the macroscopic situation, the pressure density functional is written as a virial expansion in terms of the density. [ABSTRACT FROM AUTHOR]

With the density functional theory outlined in paper I, we address and formally solve the nonlinear inversion problem associated with identifying the entropy density functional for systems with bonding constraints. With this development, we derive a nonlinear integral equation for the average site density fields of a polyatomic system. When external potential fields are set to zero, the integral equation represents a mean field theory for symmetry breaking and thus phase transformations of polyatomic systems. In the united atom limit where the intramolecular interaction sites become coincident, the mean field theory becomes identical to that developed for simple atomic systems by Ramakrishnan, Yussouff, and others. When the external potential fields are particle producing fields (in the sense introduced long ago by Percus), the integral equation represents a theory for the solvation of a simple spherical solute by a polyatomic solvent. In the united atom limit for the solvent, the theory reduces to the hypernetted chain (HNC) integral equation. This reduction is not found with the so-called ‘‘extended’’ RISM equation; indeed, the extended RISM equation—the theory in which the HNC closure of simple systems is inserted directly into the Chandler–Andersen (i.e., RISM or SSOZ) equation—behaves poorly in the united atom limit. The integral equation derived herein with the density functional approach however suggests a rational closure of the RISM equation which does pass over to the HNC theory in the united atom limit. The new integral equation for pair correlation functions arising from this suggested closure is presented and discussed. [ABSTRACT FROM AUTHOR]

This paper outlines a program for the systematic treatment of correlation effects within density functional approaches to many-electron systems. This strategy is motivated by the observation that the ground state energy of an inhomogeneous electron gas is a functional of the many-body Hartree electron density. This fact is proved, and it is outlined how the functional can be constructed at any order of perturbation theory. Second order correlation contributions to the energy are discussed as an explicit example. [ABSTRACT FROM AUTHOR]

The five points of criticism in Wesolowski's comment can be separated into three categories. Two issues are related to the question whether the nonadditive kinetic-energy functional or its functional derivative should be investigated, which is a matter of personal choice of research subject. Another issue is an unfounded accusation addressing the numerical soundness of our data. Finally, the remaining two points do not concern our paper, but deal with connections between previous work by two of us [J. Chem. Phys. 126, 234116 (2007)] and by Wesolowski and co-workers [J. Chem. Phys.129, 074107 (2008)], which we clarify in this response. Issues from all three categories have in common that they do not question the usefulness of our paper, or criticize any of our results or conclusions. [ABSTRACT FROM AUTHOR]

In the foregoing Comment [Sommerfeld[J. Chem. Phys.125, 024307 (2006)] suggests that the computational results presented in the above referenced paper does not support the conclusion of the paper regarding the prevalence of both surface- and interior-bound electron states for (H2O)14- clusters in experiments. Herein, the author presents the method used in the selection of clusters and provide experimental results that are consistent with the findings of the paper. [ABSTRACT FROM AUTHOR]

This paper proposes combining non-Boltzmann sampling with free energy perturbation to allow calculations of the free energy of hydration of a solute with both solute-water and water-water interactions with the nearest waters calculated by high-level quantum models. The method involves simulation of an approximate model of all interactions and uses both free energy perturbation and non-Boltzmann sampling to calculate the difference in energy between the approximate and quantum models. [ABSTRACT FROM AUTHOR]

The electric g-tensor is a central quantity for the interpretation of electron paramagnetic resonance spectra. In this paper, a detailed derivation of the 1-electron contributions to the g-tensor is presented in the framework of linear response theory and the second-order Douglas-Kroll-Hess (DKH) transformation. Importantly, the DKH transformation in the presence of a magnetic field is not unique. Whether or not the magnetic field is included in the required Foldy-Wouthuysen transformation, different transformation matrices and, consequently, Hamiltonians result. In this paper, a detailed comparison of both approaches is presented, paying particular attention to the mathematical properties of the resulting Hamiltonians. In contrast to previous studies that address the g-tensor in the framework of DKH theory, the resulting terms are compared to those of the conventional Pauli theory and are given a physical interpretation. Based on these mathematical and physical arguments, we establish that the proper DKH transformation for systems with constant magnetic fields is based on a gauge-invariant Foldy-Wouthuysen transformation, i.e., a Foldy-Wouthuysen transformation including the magnetic field. Calculations using density functional theory (DFT) are carried out on a set of heavy, diatomic molecules, and a set of transition-metal complexes. Based on these calculations, the performance of the relativistic calculation with and without inclusion of picture-change effects is compared. Additionally, the g-tensor is calculated for the Lanthanide dihydrides. Together with the results from the other two molecular test sets, these calculations serve to quantify the magnitude of picture-change effects and elucidate trends across the periodic table. [ABSTRACT FROM AUTHOR]

The time-dependent density functional theory (TD-DFT) calculation of excitation spectra places certain demands on the DFT exchange-correlation potential, v[sub xc], that are not met by the functionals normally used in molecular calculations. In particular, for high-lying excitations, it is crucial that the asymptotic behavior of v[sub xc] be correct. In a previous paper, we introduced a novel asymptotic-correction approach which we used with the local density approximation (LDA) to yield an asymptotically corrected LDA (AC-LDA) potential [Casida, Casida, and Salahub, Int. J. Quantum Chem. 70, 933 (1998)]. The present paper details the theory underlying this asymptotic correction approach, which involves a constant shift to incorporate the effect of the derivative discontinuity (DD) in the bulk region of finite systems, and a spliced asymptotic correction in the large r region. This is done without introducing any adjustable parameters. We emphasize that correcting the asymptotic behavior of v[sub xc] is not by itself sufficient to improve the overall form of the potential unless the effect of the derivative discontinuity is taken into account. The approach could be used to correct v[sub xc] from any of the commonly used gradient-corrected functionals. It is here applied to the LDA, using the asymptotically correct potential of van Leeuwen and Baerends (LB94) in the large r region. The performance of our AC-LDA v[sub xc] is assessed for the calculation of TD-DFT excitation energies for a large number of excitations, including both valence and Rydberg states, for each of four small molecules: N[sub 2], CO, CH[sub 2]O, and C[sub 2]H[sub 4]. The results show a significant improvement over those from either the LB94 or the LDA functionals. This confirms that the DD is indeed an important element in the design of functionals. The quality of TDLDA/LB94 and TDLDA/AC-LDA oscillator strengths were also assessed in what we believe to be the first rigorous assessment ... [ABSTRACT FROM AUTHOR]

Density functional theory using B3LYP functional predicts the structural and IR spectral features of N2O5 accurately. The disagreement between DFT and observed IR frequencies reported in a recent paper is due to incorrect vibrational assignment. Agreement between the calculated observed isotope shifts indicates that the major product of the reaction between NO2 and 18O3 is more likely NO2–O–NO18O instead of NO2–18O–NO2. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper advocates development of a new class of double-hybrid (DH) density functionals where the energy is fully orbital optimized (OO) in presence of all correlation, rather than using a final non-iterative second order perturbative correction. The resulting OO-DH functionals resolve a number of artifacts associated with conventional DH functionals, such as first derivative discontinuities. To illustrate the possibilities, two non-empirical OO-DH functionals are obtained from existing DH functionals based on PBE: OO-PBE0-DH and OO-PBE0-2. Both functionals share the same functional form, with parameters determined on the basis of different physical considerations. The new functionals are tested on a variety of bonded, non-bonded and symmetry-breaking problems. [ABSTRACT FROM AUTHOR]

In recent papers [A. D. Becke, J. Chem. Phys. 138, 074109 (2013); ibid. 138, 161101 (2013)], a density functional for strong correlations in quantum chemistry was introduced. The functional is designed to capture molecular dissociation limits using symmetry-restricted orbitals. Here we demonstrate that the functional describes, with good accuracy, two-determinant multi-reference states. The examples of this work involve 50/50 mixing of symmetry-equivalent Slater determinants at avoided crossings. We employ exactly-computed exchange and fractional spin-orbital occupancies. The connection with dissociated systems and single-determinant reference states is explained. [ABSTRACT FROM AUTHOR]

This paper explores the possibility of combining projected Hartree-Fock and density functional theories for treating static and dynamic correlations in molecular systems with mean-field computational cost. The combination of spin-projected unrestricted Hartree-Fock (SUHF) with the TPSS correlation functional (SUHF+TPSS) yields excellent results for non-metallic molecular dissociations and singlet-triplet splittings. However, SUHF+TPSS fails to provide the qualitatively correct dissociation curve for the notoriously difficult case of the chromium dimer. By tuning the TPSS correlation parameters and adding complex conjugation symmetry breaking and restoration to SUHF, the right curve shape for Cr2 can be obtained; unfortunately, such a combination is found to lead to overcorrelation in the general case. [ABSTRACT FROM AUTHOR]

Transport properties of molecular junctions are notoriously expensive to calculate with ab initio methods, primarily due to the semi-infinite electrodes. This has led to the introduction of different approximation schemes for the electrodes. For the most popular metals used in experiments, such as gold, the wide-band limit (WBL) is a particularly efficient choice. In this paper, we investigate the performance of different WBL schemes relative to more sophisticated approaches including the fully self-consistent non-equilibrium Green's function method. We find reasonably good agreement between all schemes for systems in which the molecule (and not the metal-molecule interface) dominates the transport properties. Moreover, our implementation of the WBL requires negligible computational effort compared to the ground-state density-functional theory calculation of a molecular junction. We also present a new approximate but efficient scheme for calculating transport with a finite bias. Provided the voltage drop occurs primarily inside the molecule, this method provides results in reasonable agreement with fully self-consistent calculations. [ABSTRACT FROM AUTHOR]

The key characteristics of electronic excitations of many-electron systems, the excitation energies ωα and the oscillator strengths fα, can be obtained from linear response theory. In one-electron models and within the adiabatic approximation, the zeros of the inverse response matrix, which occur at the excitation energies, can be obtained from a simple diagonalization. Particular cases are the eigenvalue equations of time-dependent density functional theory (TDDFT), time-dependent density matrix functional theory, and the recently developed phase-including natural orbital (PINO) functional theory. In this paper, an expression for the oscillator strengths fα of the electronic excitations is derived within adiabatic response PINO theory. The fα are expressed through the eigenvectors of the PINO inverse response matrix and the dipole integrals. They are calculated with the phase-including natural orbital functional for two-electron systems adapted from the work of Lowdin and Shull on two-electron systems (the phase-including Löwdin-Shull functional). The PINO calculations reproduce the reference fα values for all considered excitations and bond distances R of the prototype molecules H2 and HeH+ very well (perfectly, if the correct choice of the phases in the functional is made). Remarkably, the quality is still very good when the response matrices are severely restricted to almost TDDFT size, i.e., involving in addition to the occupied-virtual orbital pairs just (HOMO+1)-virtual pairs (R1) and possibly (HOMO+2)-virtual pairs (R2). The shape of the curves fα(R) is rationalized with a decomposition analysis of the transition dipole moments. [ABSTRACT FROM AUTHOR]

We recently proposed a linear-scaling evaluation scheme for the second-order Mo\ller-Plesset perturbation (MP2) energy based on the divide-and-conquer (DC) method [M. Kobayashi, Y. Imamura, and H. Nakai, J. Chem. Phys. 127, 074103 (2007)]. In this paper, we propose an approximate but effective expression for the first derivative of the DC-MP2 energy. The present scheme evaluates the one- and two-body density matrices, which appear in the MP2 gradient formula, in the DC manner; that is, the entire matrix is obtained as the sum of subsystem matrices masked by the partition matrix. Therefore, the method requires solving only the local Z-vector equations. Illustrative applications to three types of systems, peptides, Si surface model, and delocalized polyenes, reveal the effectiveness of the present method. [ABSTRACT FROM AUTHOR]

It is a well recognized difficult task to simulate the vibrational dynamics of ices using the density functional theory (DFT), and there has thus been rather limited success in modelling the inelastic neutron scattering (INS) spectra for even the simplest structure of ice, ice Ih, particularly in the translational region below 400 cm-1. The reason is partly due to the complex nature of hydrogen bonding (H-bond) among water-water molecules which require considerable improvement of the quantum mechanical simulation methods, and partly owing to the randomness of protons in ice structures which often requires simulation of large super-lattices. In this report, we present the first series of successful simulation results for ice Ih using DFT methods. On the basis of the recent advancement in the DFT programs, we have achieved for the first time theoretical outcomes that not only reproduce the rotational frequencies between 500 to 1200 cm-1 for ice Ih, but also the two optic peaks at ∼240 and 320 cm-1 in the translational region of the INS spectra [J. C. Li, J. Chem. Phys 105, 6733 (1996)]. Besides, we have also investigated the impact of pairwise configurations of H2O molecules on the H-bond and found that different proton arrangements of pairwise H2O in the ice Ih crystal lattice could not alter the nature of H-bond as significantly as suggested in an early paper [J. C. Li and D. K. Ross, Nature (London) 365, 327 (1993)], i.e., reproducing the two experimental optic peaks do not need to invoke the two H-bonds as proposed in the previous model which led to considerable debates. The results of this work suggest that the observed optic peaks may be attributed to the coupling between the two bands of H-O stretching modes in H2O. The current computational work is expected to shed new light on the nature of the H-bonds in water, and in addition to offer a new approach towards probing the interaction between water and biomaterials for which H-bond is essential. [ABSTRACT FROM AUTHOR]

The interplay between electron-electron and electron-proton correlation is investigated within the framework of the nuclear-electronic orbital density functional theory (NEO-DFT) approach, which treats electrons and select protons quantum mechanically on the same level. Recently two electron-proton correlation functionals were developed from the electron-proton pair densities obtained from explicitly correlated wavefunctions. In these previous derivations, the kinetic energy contribution arising from electron-proton correlation was neglected. In this paper, an electron-proton correlation functional that includes this kinetic energy contribution is derived using the adiabatic connection formula in multicomponent DFT. The performance of the NEO-DFT approach using all three electron-proton correlation functionals in conjunction with three well-established electronic exchange-correlation functionals is assessed. NEO-DFT calculations with these electron-proton correlation functionals capture the increase in the hydrogen vibrational stretching frequencies arising from the inclusion of electron-electron correlation in model systems. Electron-proton and electron-electron correlation are found to be uncoupled and predominantly additive effects to the total energy for the model systems studied. Thus, electron-proton correlation functionals and electronic exchange-correlation functionals can be developed independently and subsequently combined together without re-parameterization. [ABSTRACT FROM AUTHOR]

The modification of cerium dioxide with nanoscale metal clusters is intensely researched for catalysis applications, with gold, silver, and copper having been particularly well studied. The interaction of the metal cluster with ceria is driven principally by a localised interaction between a small number of metal atoms (as small as one) and the surface and understanding the fundamentals of the interaction of metal atoms with ceria surfaces is therefore of great interest. Much attention has been focused on the interaction of metals with the (111) surface of ceria, since this is the most stable surface and can be grown as films, which are probed experimentally. However, nanostructures exposing other surfaces such as (110) show high activity for reactions including CO oxidation and require further study; these nanostructures could be modified by deposition of metal atoms or small clusters, but there is no information to date on the atomic level details of metal-ceria interactions involving the (110) surface. This paper presents the results of density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U) calculations of the adsorption of a number of different metal atoms at an extended ceria (110) surface; the metals are Au, Ag, Cu, Al, Ga, In, La, Ce, V, Cr, and Fe. Upon adsorption all metals are oxidised, transferring electron(s) to the surface, resulting in localised surface distortions. The precise details depend on the identity of the metal atom. Au, Ag, Cu each transfer one electron to the surface, reducing one Ce ion to Ce3+, while of the trivalent metals, Al and La are fully oxidised, but Ga and In are only partially oxidised. Ce and the transition metals are also partially oxidised, with the number of reduced Ce ions possible in this surface no more than three per adsorbed metal atom. The predicted oxidation states of the adsorbed metal atoms should be testable in experiments on ceria nanostructures modified with metal atoms. [ABSTRACT FROM AUTHOR]

In this paper we show how relativistic effects can be included in the time-dependent density-functional theory (DFT) for the optical response properties of nonmetallic crystals. The dominant scalar relativistic effects have been included using the zeroth-order regular approximation (ZORA) in the ground-state DFT calculations, as well as in the time-dependent response calculations. We show that this theory can also be applied to indium antimonide in the zinc-blende structure, notwithstanding the fact that it turns into a semimetal when scalar relativistic effects are included. Results are given for the band structure, the static dielectric constant ε[sub ∞] and the dielectric function ε(ω), for the various levels on which relativity can be included, i.e., nonrelativistic, only in the ground-state, or also in the response calculation. Comparisons of our calculated results are made with experiment and other theoretical investigations. With the inclusion of scalar relativistic effects, the band structure of InSb becomes semimetallic within the local density approximation and we find a deviation of 5% from experiment for the static dielectric constant. Also the dielectric function is improved and the spectra are in good agreement with experiment, although the spectral features are shifted to somewhat lower energies compared to experiment. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Performing electronic structure calculations for large systems, such as nanoparticles or metal clusters, via orbital based Hartree-Fock or Kohn-Sham theories is computationally demanding. To study such systems, therefore, we have taken recourse to the hydrodynamic approach to time-dependent density-functional theory. In this paper we develop a variation-perturbation method within this theory in terms of the particle and current densities of a system. We then apply this to study the linear and nonlinear response properties of alkali metal clusters within the spherical jellium background model. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The interface between the [001] face of crystalline aluminum and the coexisting liquid has been studied in an ab initio molecular dynamics simulation using the orbital-free density functional description of the electronic structure. Direct observation of the equilibrium condition gives a melting temperature in excellent agreement with that obtained from the thermodynamic considerations described in the preceding paper [J. Chem. Phys. 113, 5924 (2000)]. With the resolution which can be achieved, no Friedel-type oscillations in the electron density across the interface can be seen. The atomic density profile shows two or three layers extending into the fluid. The first atomic layer beyond that at which the average atomic density falls to the bulk liquid value shows appreciable in-plane order. Monitoring the instantaneous in-plane "scattering intensity" shows that this layer fluctuates in and out of an ordered state on a time scale of picoseconds. In-plane atomic diffusion is slightly faster than interplane diffusion for these first liquid layers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper the ab initio potential of mean force for the formic acid-water system is calculated in a Monte Carlo simulation using a classical fluctuating charge molecular mechanics potential to guide Monte Carlo updates. The ab initio energies in the simulation are calculated using density-functional theory (DFT) methods recently developed by Salahub et al. [J. Chem. Phys. 107, 6770 (1997)] to describe hydrogen-bonded systems. Importance sampling methods are used to investigate structural changes and it is demonstrated that using a molecular mechanics importance function can improve the efficiency of a DFT simulation by several orders of magnitude. Monte Carlo simulation of the system in a canonical ensemble at T=300 K reveals two chemical processes at intermediate time scales: The rotation of the H[sub 2]O bonded to HCOOH, which takes place on a time scale of 3 ps, and the dissociation of the complex which occurs in 24 ps. It is shown that these are the only important structural "reactions" in the formic acid-water cluster which take place on a time scale shorter than the double transfer of the proton. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polyradicals comprised of m-phenylene-bridged organic radicals are well known as building blocks of organic ferromagnets, in which radical groups are connected with each other at the meta position in the benzene ring, and the parallel-spin configurations between radical sites are more stabilized than the antiparallel ones. Topological rules for spin alignments enable us to design organic high-spin dendrimers and polymers with the ferromagnetic ground states by linking various radical species through an m-phenylene unit. However, no systematic ab initio treatment of such spin dendrimers and magnetic polymers has been reported until now, though experimental studies on these materials have been performed extensively in the past ten years. As a first step to examine the possibilities of ferromagnetic dendrimers and polymers constructed of m-phenylene units with organic radicals, we report density functional and molecular orbital calculations of six m-phenylene biradical units with radical substituents and polycarbenes linked with an m-phenylene-type network. The relative stability between the spin states and spin density population are estimated by BLYP or B3LYP and Hartree-Fock calculations in order to clarify their utility for constructions of large spin denderimers and periodic magnetic polymers, which are final targets in this series of papers. It is shown that neutral polyradicals with an m-phenylene bridge are predicted as high-spin ground-state molecules by the computations, while m-phenylene-bridged ion-radical species formed by doping may have the low-spin ground states if zwitterionic configurations play significant roles to stabilize low-spin states. Ab initio computations also show an important role of conformations of polyradicals for stabilization of their high-spin states. The computational results are applied to molecular design of high-spin dendrimers and polymers. Implications of them are also discussed in relation to recent experimental resu... [ABSTRACT FROM AUTHOR]

Recently, we introduced a new density-functional theory (DFT) approach for the calculation of NMR shielding constants. First, a hybrid DFT calculation (using 5% exact exchange) is performed on the molecule to determine Kohn-Sham orbitals and their energies; second, the constants are determined as in nonhybrid DFT theory, that is, the paramagnetic contribution to the constants is calculated from a noniterative, uncoupled sum-over-states expression. The initial results suggested that this semiempirical DFT approach gives shielding constants in good agreement with the best ab initio and experimental data; in this paper, we further validate this procedure, using London orbitals in the theory, having implemented DFT into the ab initio code DALTON. Calculations on a number of small and medium-sized molecules confirm that our approach produces shieldings in excellent agreement with experiment and the best ab initio results available, demonstrating its potential for the study of shielding constants of large systems. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A critical comparison among recently proposed methods for evaluating the condensed Fukui function neglecting relaxation effects is presented. The sign of the condensed Fukui function is discussed and arguments for a positive definite condensed Fukui function are given. Our numerical calculations in two series of molecules show that: (i) the condensed Fukui function can give, in general, valuable information about the site selectivity in chemical reactions and systematization in a family of molecules. In particular, it has been shown that the selectivity towards protonation in anilines and derivatives molecules can be correctly assessed by the electrophilic Fukui function described in this paper. Within this approach non-negative values for the condensed Fukui function are obtained for the relevant protonation sites in these polyfunctional systems; and (ii) the solvent effects on the condensed Fukui function are negligible, confirming a recently presented theoretical prediction. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We reply to the comment on our paper "Four-component relativistic density functional calculations of heavy diatomic molecules" [J. Chem. Phys. 112, 3499 (2000)] in which the values of our calculated spectroscopic constants for heavy diatomic molecules were reinvestigated. We point out that the improved spectroscopic constants presented by Liu and van Wu¨llen confirm our basic conclusion that the generalized gradient approximations tend to overcorrect errors of the bond lengths calculated by the local density approximation for molecules with heavy constituents. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper presents static polarizabilities, polarizability anisotropies, second hyperpolarizabilities, and an analysis of the vibrational effects for these polarizabilities of azabenzenes calculated in the framework of density functional theory. All molecular geometries were fully optimized. The calculations of the polarizabilities and second hyperpolarizabilities have been performed using a finite field approach implemented in the density functional program ALLCHEM. The calculations were of all-electron type using a local exchange-correlation functional. The calculated polarizabilities are in excellent quantitative agreement with available experimental data. The effect of the replacement of CH groups by N atoms is discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Complete and detailed experimental transition probability density functions P(E[sup ′],E) have been determined for the first time for collisions between a large, highly vibrationally excited molecule, toluene, and several bath gases. This was achieved by applying the method of kinetically controlled selective ionization (KCSI) (Paper I [J. Chem. Phys. 112, 4076 (2000), preceding article]). An optimum P(E[sup ′],E) representation is recommended (monoexponential with a parametric exponent in the argument) which uses only three parameters and features a smooth behavior of all parameters for the entire set of bath gases. In helium, argon, and CO[sub 2] the P(E[sup ′],E) show relatively increased amplitudes in the wings--large energy gaps |E[sup ′]-E|--which can also be represented by a biexponential form. The fractional contribution of the second exponent in these biexponentials, which is directly related to the fraction of the so-called "supercollisions," is found to be very small (<0.1%). For larger colliders the second term disappears completely and the wings of P(E[sup ′],E) have an even smaller amplitude than that provided by a monoexponential form. At such low levels, the second exponent is therefore of practically no relevance for the overall energy relaxation rate. All optimized P(E[sup ′],E) representations show a marked linear energetic dependence of the (weak) collision parameter α[sub 1](E), which also results in an (approximately) linear dependence of 〈ΔE〉 and of the square root of 〈ΔE[sup 2]〉. The energy transfer parameters presented in this study form a new benchmark class in certainty and accuracy, e.g., with only 2%-7% uncertainty for our 〈ΔE〉 data below 25 000 cm-1. They should also form a reliable testground for future trajectory calculations and theories describing collisional energy transfer of polyatomic molecules. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper presents a methodology with which to study the local density distributions in molecular liquids and their fluctuations in any spatial direction. The distinct part of the van Hove density-density correlation function for liquid water is calculated in molecular dynamics simulations. Because of the pronounced nonspherical intermolecular interactions this pair-density function is direction dependent in the local molecular frame. We explicitly resolve the distinct van Hove function in the local frame of water molecules. The dynamics of the tetrahedrally coordinated (hydrogen bonded) and the interstitial molecules in liquid water are examined. The spectrum of the pair-density fluctuations for the tetrahedrally coordinated molecules in supercooled and ambient water exhibits a well-known translational mode at 200 cm-1 and a collective relaxation mode at lower frequencies, at approximately 10 cm-1 at 263 K. The correlation time of this relaxation process decreases with temperature, from 2.2 ps at 238 K to 1.4 ps at 298 K. The spectrum for the interstitial coordination also features a 10 cm-1 mode. It represents a secondary relaxation process in water different from a much slower Debye process. As temperature increases this relaxation mode tends to disappear from the pair-density fluctuations. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A coupled system of two molecules bearing spins of 1/2, which are allowed to diffuse relative to each other, is considered. By using a symmetry-adapted basis operator set, the overall density matrix equation is decoupled into two equations for the time-resolved isochromat components, the sum of which yields the observed signal. The appropriate stochastic Liouville equation is solved by a combination of eigenfunction expansion and finite-differences for the angular and radial relative motions, respectively. A full range of spectra from classic Pake patterns in the rigid limit to motionally narrowed Lorentzians is recovered. As an extension of the above approach, the solid-echo experiment is described in terms of the ensemble-averaged isochromats. Homogeneous transverse relaxation times (T[sub 2]) as a function of the translational diffusion coefficient (D[sub T]) are obtained from simulating SECSY (spin-echo correlation spectroscopy) signals, which show distinct T[sub 2] minima vs D[sub T]. The present method of separating the quantum and stochastic classical variables constitutes a useful approach for treating multiquantum statistical systems, and it can be generalized to an arbitrary number of spins as shown in a companion paper. In the present study we obtained the usual linear dependence of T[sub 2] on D[sub T] in the motional narrowing (or Redfield) limit, whereas in the slow motional regime a D[sub T][sup -1/2] dependence is observed, consistent with studies of rotational diffusion. Varying the distance of maximum separation between the two spins (r[sub max]) has virtually no effect on the location of the T[sub 2] minimum with respect to D[sub T], implying that the onset of slow motion is essentially independent of r[sub max]. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Many experimental studies of protein deposition on solid surfaces involve alternating adsorption/desorption steps. In this paper, we investigate the effect of a desorption step (separating two adsorption steps) on the kinetics, the adsorbed-layer structure, and the saturation density. Our theoretical approach involves a density expansion of the pair distribution function and an application of an interpolation formula to estimate the saturation density as a function of the density at which the desorption process commences, ρ[sub 1], and the density of the depleted configuration, ρ[sub 2]. The theory predicts an enhancement of the saturation density compared with that of a simple, uninterrupted random sequential adsorption (RSA) process and a maximum in the saturation density when ρ[sub 2]=(2/3)ρ[sub 1]. The theoretical results are in qualitative and semiquantitative agreement with the results of numerical simulations. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The comment presents numerical results indicating that the gauge dependence of the SOS method is not a practical problem. This gauge dependence was analyzed in the paper commented on, and the theoretical analysis therein remains valid. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]