First-Principles Simulations of Liquid Water Using a Dielectric-Dependent Hybrid Functional.

We carried out first-principles simulations of liquid water under ambient conditions using a dielectric-dependent hybrid functional, where the fraction of exact exchange is set equal to the inverse of the high-frequency dielectric constant of the liquid. We found excellent agreement with experiment for the oxygen-oxygen partial correlation function at the experimental equilibrium density and 311 ± 3 K. Other structural and dynamical properties, such as the diffusion coefficient, molecular dipole moments, and vibrational spectra, are also in good agreement with experiment.

Electron affinity of liquid water.

Understanding redox and photochemical reactions in aqueous environments requires a precise knowledge of the ionization potential and electron affinity of liquid water. The former has been measured, but not the latter. We predict the electron affinity of liquid water and of its surface from first principles, coupling path-integral molecular dynamics with ab initio potentials, and many-body perturbation theory.

Local and Global Effects of Dissolved Sodium Chloride on the Structure of Water.

Determining how the structure of water is modified by the presence of salts is instrumental to understanding the solvation of biomolecules and, in general, the role played by salts in biochemical processes. However, the extent of hydrogen bonding disruption induced by salts remains controversial. We performed extensive first-principles simulations of solutions of a simple salt (NaCl) and found that, while the cation does not significantly change the structure of water beyond the first solvation shell, the anion has a further reaching effect, modifying the hydrogen-bond network even outside its second solvation shell.

Photoelectron Spectra of Aqueous Solutions from First Principles.

We present a combined computational and experimental study of the photoelectron spectrum of a simple aqueous solution of NaCl. Measurements were conducted on microjets, and first-principles calculations were performed using hybrid functionals and many-body perturbation theory at the G0W0 level, starting with wave functions computed in ab initio molecular dynamics simulations. We show excellent agreement between theory and experiments for the positions of both the solute and solvent excitation energies on an absolute energy scale and for peak intensities.

Density and Compressibility of Liquid Water and Ice from First-Principles Simulations with Hybrid Functionals.

We determined the equilibrium density and compressibility of water and ice from first-principles molecular dynamics simulations using gradient-corrected (PBE) and hybrid (PBE0) functionals. Both functionals predicted the density of ice to be larger than that of water, by 15 (PBE) and 35% (PBE0). The PBE0 functional yielded a lower density of both ice and water with respect to PBE, leading to better agreement with experiment for ice but not for liquid water.

Temperature-cycle microscopy reveals single-molecule conformational heterogeneity.

Our previous temperature-cycle study reported FRET transitions between different states on FRET-labeled polyprolines [Yuan et al., PCCP, 2011, 13, 1762]. The conformational origin of such transitions, however, was left open.

[Diagnosis and treatment of headache combined with orthopedic disorders in children and adolescents].

To study characteristics of headache combined with orthopedic disorders in children and adolescents and to develop treatment approaches, we examined 116 patients aged from 5 to 17 years. Headache of tension was found in 89 (77%) and chronic headache in 27 (23%) patients. Along with clinical/neurological and orthopedic examination, all patients were studied using a special device that allowed to quantitatively measure the bearing (in three dimensions) and biomechanic body balance.

Removal of Basis-Set Artifacts in Kohn-Sham Potentials Recovered from Electron Densities.

Kohn-Sham effective potentials recovered from Gaussian-basis-set electron densities exhibit large oscillations and asymptotic divergences not found in exact potentials and in functional derivatives of approximate density functionals. We show that the detailed structure of these oscillations and divergences is almost exclusively determined by the basis set in terms of which the reference density is expressed, and is almost independent of the density-functional or wave function method used for computing the density. Based on this observation, we propose a smoothening scheme in which most basis-set artifacts in a Kohn-Sham potential recovered from a given density are removed by subtracting the oscillation profile of the exchange-only local-density approximation potential computed in the same basis set as the reference density.

Efficient construction of exchange and correlation potentials by inverting the Kohn-Sham equations.

Given a set of canonical Kohn-Sham orbitals, orbital energies, and an external potential for a many-electron system, one can invert the Kohn-Sham equations in a single step to obtain the corresponding exchange-correlation potential, vXC(r). For orbitals and orbital energies that are solutions of the Kohn-Sham equations with a multiplicative vXC(r) this procedure recovers vXC(r) (in the basis set limit), but for eigenfunctions of a non-multiplicative one-electron operator it produces an orbital-averaged potential. In particular, substitution of Hartree-Fock orbitals and eigenvalues into the Kohn-Sham inversion formula is a fast way to compute the Slater potential.

Improved electronic excitation energies from shape-corrected semilocal Kohn-Sham potentials.

We propose a general method for obtaining accurate valence and Rydberg excitation energies from standard density-functional approximations in adiabatic linear-response time-dependent density-functional theory. The method consists in modeling the sum of Hartree (Coulomb) and exchange-correlation potentials, v(HXC)(r), by the Hartree-exchange-correlation potential of the corresponding partially ionized system in which a fraction of electron charge (δ = 0.15 to 0.

Luminescence quantum yield of single gold nanorods.

We study the luminescence quantum yield (QY) of single gold nanorods with different aspect ratios and volumes. Compared to gold nanospheres, we observe an increase of QY by about an order of magnitude for particles with a plasmon resonance >650 nm. The observed trend in QY is further confirmed by controlled reshaping of a single gold nanorod to a spherelike shape.

A generalized gradient approximation for exchange derived from the model potential of van Leeuwen and Baerends.

The common way to obtain energies from Kohn-Sham exchange potentials is by using the Levy-Perdew virial relation. For potentials that are not functional derivatives (i.e.

Absorption, luminescence, and sizing of organic dye nanoparticles and of patterns formed upon dewetting.

Organic nanoparticles made of a push-pull triarylamine dye with an average diameter of 60 nm, were prepared by reprecipitation. We study their photophysical properties by a combination of photothermal and fluorescence microscopy. Photothermal contrast provides a quantitative measure of the number of absorbers.

Correlated absorption and photoluminescence of single gold nanoparticles.

We perform simultaneous absorption (photothermal) and fluorescence detection of gold nanospheres with diameters of 80, 60, 40, 20, 10, and 5 nm. We unambiguously identify the same individual nanoparticles (NPs) over large areas (>400 μm(2)) by means of atomic force microscopy (AFM) and optical absorption (photothermal) microscopy. We correlate the height of NPs measured with AFM with absorption and fluorescence signals from the same individual NPs.

Making gold nanoparticles fluorescent for simultaneous absorption and fluorescence detection on the single particle level.

We demonstrate a simple way of making individual 20 nm gold nanoparticles fluorescent (with a fluorescence quantum yield of about 10(-6)) in glycerol. Gold NPs prepared in such a way have bright fluorescence for a long time under moderate excitation, and their fluorescence remains when the solvent is exchanged to water. We propose to use these nanoparticles as a calibration standard for simultaneous detection of fluorescence and absorption (by means of photothermal detection), and experimentally demonstrate the theoretically predicted shift in axial positions of these signals.

Room-temperature detection of a single molecule's absorption by photothermal contrast.

So far, single-molecule imaging has predominantly relied on fluorescence detection. We imaged single nonfluorescent azo dye molecules in room-temperature glycerol by the refractive effect of the heat that they release in their environment upon intense illumination. This photothermal technique provides contrast for the absorbing objects only, irrespective of scattering by defects or roughness, with a signal-to-noise ratio of ~10 for a single molecule in an integration time of 300 milliseconds.

Communication: Explicit construction of functional derivatives in potential-driven density-functional theory.

We propose a method for imposing an important exact constraint on model Kohn-Sham potentials, namely, the requirement that they be functional derivatives of functionals of the electron density ρ. In particular, we show that if a model potential v(r) involves no ingredients other than ρ, ∇ρ, and ∇(2)ρ, then the necessary and sufficient condition for v(r) to be a functional derivative is ∂v/∂∇ρ=∇(∂v/∂∇(2)ρ). Integrability conditions of this type can be used to construct functional derivatives without knowing their parent functionals.

How to tell when a model Kohn-Sham potential is not a functional derivative.

A model exchange-correlation potential constructed with Kohn-Sham orbitals should be a functional derivative of some density functional. Several necessary conditions for a functional derivative are discussed including: (i) minimization of the total-energy expression by the ground-state solution of the Kohn-Sham equations, (ii) path independence of the van Leeuwen-Baerends line integral, and (iii) net zero force and zero torque on the density. A number of existing model potentials are checked for these properties and it is found that most of the potentials tested are not functional derivatives.

Reconstruction of Density Functionals from Kohn-Sham Potentials by Integration along Density Scaling Paths.

We demonstrate by specific examples that if a Kohn-Sham exchange-correlation potential is given explicitly in terms of the electron density and its derivatives, then one can easily reconstruct the parent density functional by evaluating analytically (or numerically with one-dimensional quadratures) the van Leeuwen-Baerends line integral (Phys. Rev. A 1995, 51, 170-178) along a path of (coordinate)-scaled densities.

Virial exchange energies from model exact-exchange potentials.

It is shown by the example of Slater's averaged exchange potential that a poor approximation to the optimized effective potential (OEP) can yield a deceptively accurate energy via the conventional Kohn-Sham energy functional. For a trial exchange potential to be correct, its Kohn-Sham energy must coincide with the value obtained by the Levy-Perdew virial relation. Significant discrepancies between Kohn-Sham and the virial exchange energies are found for self-consistent Slater, Becke-Johnson, and effective local potentials (ELPs); their relative magnitudes are used to argue that, as approximations to the exact-exchange OEP, ELPs are the most accurate.

Fluorescence detection with high time resolution: from optical microscopy to simultaneous force and fluorescence spectroscopy.

Picosecond time-resolution fluorescence signal detection over many hours is possible using the time-correlated single photon counting (TCSPC) technique. Advanced TCSPC with clock oscillator set by the pulsed laser and data analysis provides a tool to investigate processes in single molecules on time scale from picoseconds to seconds. Optical imaging techniques combined with TCSPC allow one to study the spatial distribution of fluorescence properties in solution and on a surface.

Separating structural heterogeneities from stochastic variations in fluorescence resonance energy transfer distributions via photon distribution analysis.

We establish a probability distribution analysis (PDA) method for the analysis of fluorescence resonance energy transfer (FRET) signals to determine with high precision the originating value of a shot-noise-limited signal distribution. PDA theoretical distributions are calculated explicitly including crosstalk, stochastic variations, and background and represent the minimum width that a FRET distribution must have. In this way an unambiguous distinction is made between shot-noise distributions and distributions broadened by heterogeneities.

Optical characteristics of atomic force microscopy tips for single-molecule fluorescence applications.

Knowledge of the optical properties of atomic force microscopy (AFM) tips is relevant for the combination of optical and force spectroscopy. The luminescence properties of five commercial AFM tips were characterized using a combination of multiparameter fluorescence detection (MFD) and scanning confocal techniques. These include three Si3N4 tips, one silicon tip, and one high-density carbon (HDC) tip grown on top of a silicon tip.

Pericardioscopic implantation of electrodes for myocardial electrocardiostimulation.

Endocardial placement of electrodes for myocardial electrostimulation is a standard procedure. In the past, myocardial electrode placement was not performed routinely mainly because of the trauma of surgical access to the heart. We have developed for the first time an endoscopic approach.

[Specifics of diagnostic and surgical approach in the treatment of complicated injuries of the extremities in the acute period].

The results of treatment of 82 patients with associated injury to the nerves of the extremities have been analysed. In rupture of a nerve, the clinico-neurologic examination has the most informative value, in its partial injury, the performance of electrophysiologic investigations is mandatory. A degree of restoration of the extremity function depends on timeliness and adequacy of the operation.