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A systematic analysis of the orbital populations of a structurally complex organometallic complex has been carried out in the Mulliken approximation using more than a hundred popular computing methods with basis sets extended with polarization and diffuse wave functions that are traditionally used to describe electronically-excited states and coordinative interactions. A conclusion is drawn on the limitations of the classical Mulliken approach. [ABSTRACT FROM AUTHOR]

We theoretically study biexcitons and quadrons in quantum dots with parabolic confinement and give a complete comparison between the two excitations. The calculation of quadron and biexciton binding energies as functions of electron-to-hole confinement potentials and mass ratios, using the unrestricted Hartree–Fock method, shows the essential differences between biexcitons and quadrons. The crossover between the negative and positive binding energies is indicated. The effect of an external magnetic field on the quadron and biexciton binding energies has also been investigated. In addition, the crossover between anti-binding and binding of both excited quadron and biexciton states in a certain range of the electron-to-hole oscillator length ratios has been found. [ABSTRACT FROM AUTHOR]

For the first time, charge characteristics of an organometallic complex with a radiative LMCT (ligand-to-metal charge transfer) state have been systematically evaluated using 124 methods at different levels of theory (for Ti(η5:η1-CpCMe2CB10H10C)2 taken as an example). Reliability of the results of calculation in the Mulliken approximation was considered. [ABSTRACT FROM AUTHOR]

Elastic and inelastic electron scattering form factors for the 17O nucleus are calculated for the positive parity low-lying states in the momentum transfer interval 0.05-3 fm in the framework of shell model and Skyrme-Hartree-Fock calculations. Also, protons, neutrons, mass and charges root mean square, r.m.s., radii and the charge spatial density distribution are calculated. The ZBME model space out of 12C nuclei core with rewile interaction have been used. For all selected ground and excited states, Skyrme interactions with SkXcsb and SLy4 parameter, harmonic and Wood-Saxon potentials are adopted in Hartree-Fock theory to generate the mean potential and hence calculate the elements of single-particle matrix and form factors. Also, we have used Tassie model to account for core-polarization effect. Finally, to check the reality of the calculated values, the charges r.m.s. and form factors are discussed and compared to the measured values. A good agreement can be shown by the theoretical results to the measured ones.

In many-electron systems, the exchange and correlation energies, associated with the indistinguishability and Columbic interactions among electrons, are the major cause for the inaccurate estimate of their ground state energies. In the present study, improved ground state energies of highly electronegative atoms such as F, Cl, B, Al and Sc are obtained using unrestricted Hartree–Fock method, though Hartree–Fock method does not incorporate the interactions between electrons (correlation) leading to inaccurate estimates of total energy. Nevertheless, an augmented correlation-consistent polarized valence Quintuple-Zeta functions (aug-cc-pV5Z) are used which incorporate the correlation and polarization effects in the functions. Such effects are very important in case of highly electronegative atoms. The results obtained in this study are compared with previous theoretical work and with values given in NIST tables for the ground state energies of the investigated atoms. It has been found that energies have been much improved by using aug-cc-pV5Z basis sets for the atoms under investigation. [ABSTRACT FROM AUTHOR]

In the framework of the variational Monte Carlo and the Hartree-Fock methods, the four-electron system is investigated to calculate several properties of the beryllium atom. For the beryllium atom and its isoelectronic ions, we calculated the ground-state energy eigenvalues and the energy of the compressed ground state beryllium atom in an impenetrable spherical box at different radii of the spherical box. Furthermore, the correlation energies are calculated as well. Moreover, the pressure and the kinetic energy of the confined beryllium atom are also calculated at certain radii of the spherical box. A good agreement between the calculated values and the corresponding available previous results is shown. The results obtained using the variational Monte Carlo method are slightly better than those obtained using the Hartree-Fock method. [ABSTRACT FROM AUTHOR]

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State of the art computing opens now a new window to the integer quantum Hall effect (IQHE) regime, which enforces a major revision of the common knowledge accumulated so far. In our record-breaking application of the Hartree–Fock method we use up to 3000 electrons distributed over up to 5000 states for almost macroscopic system size of 1000 × 1000 nm. In particular, the formation of compressible and in-compressible edge stripes turns out to develop essentially different from the common picture used so far. Oppositely to the theory of Chklovskii, Shklovskii and Glazman (CSG), the narrow channels, as assumed by the early models of the IQHE, do not widen up into wide compressible stripes. Instead, the wide compressible stripes of CSG transform into a mixture of clusters of full and empty spin-split LLs, while the cluster boundaries create a network of still narrow quantum channels sitting on top of the wide compressible stripes. On this background the early models based on narrow edge channels do not suffer from neglecting electron–electron interaction as falsely stated in the past. Quite oppositely, in contrast to the common believe, our modeling demonstrates that also the IQHE regime carries the hallmark of many-body physics which stabilizes narrow edge channels also in the presence of electron–electron interaction.

The paper proposes a method for preliminary transformation of the spectrum of the equation operator both in the Hartree–Fock method and in density functional theory. This method allows to solve a partial eigenvalue problem instead of the complete one, while the eigenfunctions are ordered in a way convenient for calculation. The transformation makes an old idea of grid approximation of a solution competitive in terms of computational speed as compared to widely used approaches based on basis sets methods. [ABSTRACT FROM AUTHOR]

Abstract—The main problems that appear in the quantum-chemical modeling of complex lanthanide (Ln) ions are considered. The main difficulty is the presence of an open 4f shell in Ln ions, which leads to a large number of quasi-degenerate electronic states (which cannot be correctly described by single-configuration methods). Various approaches to quantum-chemical modeling of systems containing Ln complexes are analyzed. We consider the basis sets in which 4f electrons are taken into account explicitly (4f-in-valence) and the bases in which 4f electrons are taken into account in an effective core potential (core is taken to be a certain number of electrons located near a nucleus and not involved in chemical bond formation; 4f-in-core). The quantum-chemical calculations using the Hartree–Fock methods and the density functional theory are shown to lead to an incorrect distribution of the electron density of a complex, which is typical of 4f-in-valence bases, and to an incorrect description of the coordination number of a complex ion when 4f-in-core basis sets are used. The incorrect reproduction of the structure of complexes is likely to be related to the inability to take into account the interaction of the 4f orbitals with the ligand field in a calculation. Nevertheless, we propose an approach, which consists in using the 4f-in-core basis for a samarium atom and fixing the structure of a complex. This makes it possible to obtain the correct reproduction of the composition of the first coordination sphere of a complex and the undistorted electronic structure of a complex particle. Here, good agreement between quantum-chemical modeling results and experimental data is observed. The use of 4f-in-core bases is shown to significantly decrease the machine time costs, which makes it possible to use these bases for routine calculations. This approach can be extended to other Ln-containing model systems. [ABSTRACT FROM AUTHOR]

This study applies Density Functional Theory (DFT), using the B3LYP functional, and via ab initio Restrict Hartree-Fock (RHF) methods, to study the infrared spectrum of steroid 17-Iodo-androst-16-ene. The spectrum was obtained via computational methods ab initio RHF and DFT. Optimization of molecular structure via UFF (Universal Force Field), followed by PM3 (Parametric Method 3), with geometric optimization, obtaining the spectrum of other basis sets of steroid 17-Iodo-androst-16-ene. The study this steroid was chosen because it can could act as aromatase enzyme inhibitors and this phenomenon could be translated as good compounds to treat breast cancer. The B3LYP functional always presents the lowest thermal energy than the RHF in all calculated bases, however the RHF always presents the highest Entropy than the B3LYP, in all the calculated basis sets. The normalized spectrum calculated in the B3LYP/SVP functional/basis set have harmonic frequency with peaks 3,241.83 cm-1, 100% and 3,177.53.5 cm-1 at 43.304% absorbance. The study has so far been limited to computational methods compatible with the theory of quantum chemistry. [ABSTRACT FROM AUTHOR]

Study of synthetic and natural materials suitable for the creation of nanocarriers and their modification will provide a breakthrough in the treatment of many diseases. Glycosaminoglycans (heparin and its derivatives) are a good choice for creating nanocarriers due to their unique biological and physicochemical properties. The complexation of Pr (III), Sm (III), Eu (III) with heparin anions was studied by potentiometric titration at 37°C and an ionic strength of 0,15 M NaCl. Significant forms and chemical equilibria were determined using the NewDALSFEK program. In the pH range from 2,7 to 5, a complex of the type {[LnHep]}n is formed, where Hep3- is a monomeric unit of the heparin macromolecule. Data on the stability of nanocompositions were obtained: lgβ[PrHep]=4,27±0,04, lgβ[SmHep]=4,28±0,03, lgβ[EuHep]=4,28±0,03. The M06-HF method in combination with the CSDZ+* basic set was used to perform quantum chemical modeling of the complexes.

The molecular structure of bis(2-isobutyrylamidophenyl)amine (H3LNNN) has been determined from single-crystal X-ray diffraction data. The crystal packing of H3LNNN is governed by the N-H···O and C-H···O hydrogen-bonding and C-H···p stacking interactions between the vicinal molecules. The intermolecular interactions in the crystal structure of H3LNNN have been also examined via Hirshfeld surface analysis and fingerprint plots. The Hirshfeld surface analysis showed that the important role of N-H···O and C-H···p interactions in the solid-state structure of H3LNNN. The molecular structure, vibrational frequencies, and infrared intensities of H3LNNN were computed by ab initio HF and DFT (B3LYP, B3PW91, and BLYP) methods using the 6-31G(d,p) basis set. The computed theoretical geometric parameters were compared with the corresponding single crystal structure of H3LNNN. The harmonic vibrations calculated for the title compound by the B3LYP method are in good agreement with the experimental IR spectral data. The theoretical vibrational spectrum of the H3LNNN compound was interpreted through potential energy distributions using the SQM Version 2.0 program. The performance of the used methods and the scaling factor values were calculated with PAVF Version 1.0 program. [ABSTRACT FROM AUTHOR]

The hydration of the basal surfaces of kaolinite is studied by theoretical methods. The cluster method was used to simulate the positions of atoms. The positions of the atoms of the basal surfaces of dry and hydrated minerals are optimized by minimizing the total energy in the Hartree–Fock approximation. The adsorption energies of water molecules were calculated taking into account the fourth-order correlation corrections of Møller–Plesset perturbation theory. The formation of the IR spectrum of kaolinite in the range of wave numbers 2500–4500 cm−1 is studied. The experimentally observed effect of the change in relative intensity and position of the band with a change in the moisture content of the sample is interpreted.

The value of exchange energy for near-surface double-donor and double-quantum dot structures under the effect of external electric field has been calculated using unrestricted Hartree–Fock method. The dependences of exchange energy on geometric parameters have been obtained. It has been found that the location of donor centers near the surface of the semiconductor leads to an increase in the exchange energy. Approximate formulas for the dependence of the exchange energy on the distance between the centers of quantum dots are suggested. It has been shown that exchange coupling control is less sensitive to electric field as compared to magnetic field, and electron density relocation at large electric fields should be taken into account when designing devices based on the structures under study. [ABSTRACT FROM AUTHOR]