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The selectivity of the sodium channel has been the subject of numerous experimental and theoretical studies. In this work, this problem is approached from a theoretical point of view based on a model built from the Selective Filter (SF) of the open structure of the voltage-activated channel of the bacterium Magnetococcus marinus. This approach has allowed us to calculate the interaction energies of the system (cation-water-SF-fragment), both for the sodium cation and the potassium cation. The results have highlighted the importance of differential dehydration of cations, as well as the environment where it occurs. Semi-empirical and ab initio methods have been applied to analyze and quantify the interaction energies when the cations are in the SF of the sodium channel, with the DFT (ab initio) methods giving us the key to the distribution of the interaction energies and therefore how dehydration occurs. [ABSTRACT FROM AUTHOR]

The competition between Na + and K + with a protein for water was investigated by using Density Functional Theory (DFT) calculations. The optimized potential energy curves have been made in the DFT, together with balanced basis sets of split valence Def2-SV(P). Initially, calculations were done in order to know the organization of the hydration shell of the sodium and potassium ions, when up to sixteen molecules of water are added. The results indicate the structure and stability of these cations with water clusters. Then, this knowledge was used for the analysis of the hydrated protein when potassium or sodium cations approach them, showing that cation has a dehydration process more favorable energetically, and indicating for which cation, potassium or sodium is the competition with the protein for water more favorable. [ABSTRACT FROM AUTHOR]

Spin-projected spin polarized Møller-Plesset and spin polarized coupled clusters calculations have been made to estimate the cyclobutadiene automerization, the ethylene torsion barriers in their ground state, and the gap between the singlet and triplet states of ethylene. The results have been obtained optimizing the geometries at MP4 and/or CCSD levels, by an extensive Gaussian basis set. A comparative analysis with more complex calculations, up to MP5 and CCSDTQP, together with others from the literature, have also been made, showing the efficacy of using spin-polarized wave functions as a reference wave function for Møller-Plesset and coupled clusters calculations, in such problems. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Highlights: [•] We study the potential energy surface of the acetone–carbon dioxide complex with ab initio methods. [•] We analyze the contributions to the interaction energy with variational and perturbative approaches. [•] We describe non-conventional structures in which dispersion energy plays a key role. [•] We show that current density functional theory methods are unsuitable to describe this type of complexes. [ABSTRACT FROM AUTHOR]

The correlation factor of Colle and Salvetti is studied by comparing the behavior of three different correlation functionals. The normalization, sum rule, Coulomb hole, correlation energy integrand, and the Wigner exclusion hole have all been analyzed by applying the three approaches. The results indicate that the correlation factor proposed by Colle–Salvetti is a very good choice for modeling electron correlation in atoms. The flaws appearing in the development of the Colle–Salvetti equations seem mainly due to an inadequate use of the first mean value theorem of integral calculus. The Gaussian summation used for the two-body density matrix seems to be a good approximation to obtain the correlation factor equations. [ABSTRACT FROM AUTHOR]

Perylenediimides (PDIs) are the focus of a huge number of research lines for their awesome properties which can be modulated over a wide range by chemical modification of their structure. However, industrial applications require reduced costs in materials preparation and transformation. In this contribution we explore the ability of sulfur-substituted PDIs to vary their electronic character from strong electron-donating to strong electron-accepting in just one reaction. [Display omitted] • Change in the UV–vis absorption depending on the oxidation state of the sulfur substituent. • Modulation of the fluorescence quantum yield with the oxidation state of the sulfur substituents. • Tunability of the electronic character of the perylenediimides as a function of the oxidation state of the sulfur atom. [ABSTRACT FROM AUTHOR]

The electronic structure of 7/9-AGNR superlattices with up to eight unit cells has been studied by means of state-of-the-art Density Functional Theory (DFT) and also by two model Hamiltonians, the first one including only local interactions (Hubbard model, Hu) while the second one is extended to allow long-range Coulomb interactions (Pariser, Parr and Pople model, PPP). Both are solved within mean field approximation. At this approximation level, our calculations show that 7/9 interfaces are better described by spin non-polarized solutions than by spin-polarized wavefunctions. Consequently, both Hu and PPP Hamiltonians lead to electronic structures characterized by a gap at the Fermi level that diminishes as the size of the system increases. DFT results show similar trends although a detailed analysis of the density of states around the Fermi level shows quantitative differences with both Hu and PPP models. Before improving model Hamiltonians, we interpret the electronic structure obtained by DFT in terms of bands of topological states: topological states localized at the system edges and extended bulk topological states that interact between them due to the long-range Coulomb terms of Hamiltonian. After careful analysis of the interaction among topological states, we find that the discrepancy between ab initio and model Hamiltonians can be resolved considering a screened long-range interaction that is implemented by adding an exponential cutoff to the interaction term of the PPP model. In this way, an adjusted cutoff distance λ = 2 allows a good recovery of DFT results. In view of this, we conclude that the correct description of the density of states around the Fermi level (Dirac point) needs the inclusion of long-range interactions well beyond the Hubbard model but not completely unscreened as is the case for the PPP model. [ABSTRACT FROM AUTHOR]

The standard procedure to identify the hole- or electron-acceptor character of amorphous organic materials used in OLEDs is to look at the values of a pair of basic parameters, namely, the ionization potential (IP) and the electron affinity (EA). Recently, using published experimental data, the present authors showed that only IP matters, i.e., materials with IP > 5.7 (<5.7) showing electron (hole) acceptor character. Only three materials fail to obey this rule. This work reports ab initio calculations of IP and EA of those materials plus two materials that behave according to that rule, following a route which describes the organic material by means of a single molecule embedded in a polarizable continuum medium (PCM) characterized by a dielectric constant ε. PCM allows to approximately describe the extended character of the system. This "compound" system was treated within density functional theory (DFT) using several combinations of the functional/basis set. In the preset work ε was derived by assuming Koopmans' theorem to hold. Optimal ε values are in the range 4.4–5.0, close to what is expected for this material family. It was assumed that the optical gap corresponds to the excited state with a large oscillator strength among those with the lowest energies, calculated with time-dependent DFT. Calculated exciton energies were in the range 0.76–1.06 eV, and optical gaps varied from 3.37 up to 4.50 eV. The results are compared with experimental data. [ABSTRACT FROM AUTHOR]

Numerous theoretical and experimental studies have attempted to determine the mechanisms of bacterial potassium channel selectivity (KcsA). However, there are still different aspects that remain uncovered. In this paper, we have built a model based on a selective filter (SF) for the KcsA, taking into account its structure and calculating the system interaction energy (cation–water–SF-fragment), using both sodium and potassium as cations. The results tell us which aspects could be responsible for the higher selectivity of the channel. All this reveals that there are two most important aspects: the dehydration of potassium in relation to sodium, and the environment where such dehydration occurs, in the entrance of the SF. Both semi-empirical and ab initio methods are applied to analyse and quantify the change of the interactions that take place when the cation K+ or Na+ crosses the SF. [ABSTRACT FROM AUTHOR]

We describe a new algorithm for the generation of 3D grids for the numerical evaluation of multicenter molecular integrals in density functional theory. First, we use the nuclear weight functions method of Becke [A. D. Becke, J. Chem. Phys. 88, 2547 (1988)] to decompose a multicenter integral ∫F(r) dr into a sum of atomic-like single-center integrals. Then, we apply automatic numerical integration techniques to evaluate each of these atomic-like integrals, so that the total integral is approximated as ∫F(r) dr≊∑iωiF(ri). The set of abscissas ri and weights ωi constitutes the 3D grid. The 3D atomic-like integrals are arranged as three successive monodimensional integrals, each of which is computed according to a recently proposed monodimensional automatic numerical integration scheme which is able to determine how many points are needed to achieve a given accuracy. When this monodimensional algorithm is applied to 3D integration, the 3D grids obtained adapt themselves to the shape of the integrand F(r), and have more points in more difficult regions.The function F(r), which, upon numerical integration, yields the 3D grid, is called the generating function of the grid. We have used promolecule densities as generating functions, and have checked that grids generated from promolecule densities are also accurate for other integrands. Our scheme is very reliable in the sense that, given a relative tolerance ε, it generates 3D grids which are able to approximate multicenter integrals with relative errors smaller than ε for all the molecules tested in this work. Coarser or finer grids can be obtained using greater or smaller tolerances. For a series of 21 molecules, the average number of points per atom for ε=2.0·10-3, ε=2.0·10-4, ε=2.0·10-5, ε=2.0·10-6, and ε=2.0·10-7 is respectively 3141 (2.9·10-4), 10271 (2.4·10-5), 27184 (3.1·10-6), 72266... [ABSTRACT FROM AUTHOR]

Recent interest in the absorption and photo-luminescence properties of a molecule with an envisioned optoelectronic use, such as TPD ( N, N $$^{\prime }$$ -diphenyl- N, N $$^{\prime }$$ -bis(3-methylphenyl)-(1,1 $$^{\prime }$$ -biphenyl)-4,4 $$^{\prime }$$ -diamine), prompted us to apply Density Functional Theory (DFT) and Time-Dependent DFT methods to obtain theoretical results in agreement with experimental findings. Based on these benchmark results, we tackled in a further step the study of a set of molecules derived from the triphenylamine moiety, trying thus to relate their structures with their expected behavior in optical devices . Therefore, we analyzed several key properties for it, like the Stokes shift (important for laser applications), or their absorption and emission spectra which, together with the energies of frontier molecular orbitals, help to determine their optical behavior. [ABSTRACT FROM AUTHOR]

A guessing game very popular in some European countries involves several players hiding in their hands a number of coins (or pebbles) between zero and three, then attempting to guess in turn the total number of coins in the hands of everyone, with the restriction that no player can repeat the guess issued by any predecessor. After a full round, the player, if any, who guesses correctly wins. Of course, rounds without a winner are also possible, in which case a new round is started afresh. The purpose of the present article is to present an analysis of this game (called Chinos in Spain, as a perturbation of “chinas”, i.e. pebbles), and some of its possible variants. Our primary aim is to show its potential to shed light on some issues of strategic behavior and information transmission that seem very germane to some social and economic problems. [ABSTRACT FROM AUTHOR]

We investigate here the lowest‐energy (spin‐conserving) excitation energies for the set of He‐Ne atoms, with the family of nonempirical PBE, PBE0, PBE0‐1/3, PBE0‐DH, PBE‐CIDH, PBE‐QIDH, and PBE0‐2 functionals, after employing a wide variety of basis sets systematically approaching the basis set limit: def2‐nVP(D), cc‐pVnZ, aug‐cc‐pVnZ, and d‐aug‐cc‐pVnZ. We find that an accuracy (ie, mean unsigned error) of 0.3 to 0.4 eV for time‐dependent density functional theory (DFT) atomic excitation energies can be robustly achieved with modern double‐hybrid methods, which are also stable with respect to the addition of a double set of diffuse functions, contrarily to hybrid versions, in agreement with recent findings employing sophisticated multiconfigurational DFT methods. [ABSTRACT FROM AUTHOR]

• Efficient methodology for post-synthetic functionalization of polyaniline with phosphorus-containing compounds. • The electroactivity of modified polyaniline depends on the phosphorus precursor. • DFT results proved that the reaction occurs through the imine groups and the phosphorus atoms. P-postmodified polyaniline was obtained by reacting phosphorus trichloride (PCl 3) and chlorodiphenylphosphine (PPh 2 Cl) and polyaniline (PANI), under mild conditions. The reaction was found to be very selective, as only the imine groups were involved in the P-functionalization, and efficient as well, affording a P-loading of 3 at.% and 5 at.% for PPh 2 Cl and PCl 3 , respectively. All the polymers were characterized by different techniques and the results were endorsed by theoretical calculations. Experimental and Density Functional Theory results proved that the reaction occurs through the imine groups and the phosphorus atoms, generating N P bonds. The electrochemical properties of the N P modified materials were evaluated and the catalytic activity towards oxygen reduction reaction was measured. It was found that a high concentration of phenyl groups from PPh 2 Cl (about 3 at.%) affected negatively the activity of the catalyst since they prevented the access of the oxygen molecules to the catalytic active sites. However, a lower amount of PPh 2 groups (1 at.%) or the use of PCl 3 avoided this hindrance and resulted in an improved catalytic activity with respect to pristine PANI. [ABSTRACT FROM AUTHOR]

The prevailing approach in density-functional theory makes use of universal functionals, valid for any number of electrons (N). In this article and following the work of Lieb [E. H. Lieb, Int. J. Quantum Chem. 24, 243 (1983)], we argue that the use of N-dependent functionals could be an equally valid approach. Size consistency (dissociation into proper fragments) puts restrictions on the form that N-dependent functionals may adopt. We propose a simple procedure for correcting the size-consistency problem of existing N-dependent functionals that also provides an original way of designing new ones. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]