A. B. Sobolev

Electronic structure of lithium tetraborate Li2B4O7 crystals. Cluster calculations and x-ray photoelectron spectroscopy

The results of an investigation of the electronic structure of lithium tetraborate crystals using experimental (x-ray photoelectron spectroscopy) and theoretical (quantum-chemical modeling) methods are reported. The experimental spectrum of the valence-band states of the crystal lies 2–15 eV below the Fermi level and is due primarily to boron-oxygen groups (B4O9). The quantum-chemical calculations were performed self-consistently, using the standard variant of the scattered-wave method in the model of a cluster embedded in a lattice of point charges. The data obtained on the partial contribution of the model densities to the one-electron spectrum of the [B4O9]6 cluster make it possible to interpret the fine structure of the experimental spectrum of the valence-band states.

Electronic structure of a LiB305 nonlinear optical crystal

The electronic bands of a LiB 3 O 5 (LBO) crystal with excellent nonlinear optical properties have been studied using the scattered-wave method in embedded-cluster model. Calculations were carried out for a [B 3 O 7 ] 5- cluster, as this anionic group is the crystal basic structural unit. The interpretation of experimental photoemission spectra is based on electronic structure cluster calculations. From calculation performed, it follows that the contribution of trigonal and tetrahedral boron-oxygen groups dominates in the electronic structure of LBO, the contribution of 2p-boron states is immaterial.

Hartree-Fock calculation of BaF2:La systems

Abstract We present the results of an investigation of the electron structures of BaF 2 , LaF 3 and BaF 2 :La crystals. The effects of lattice polarization and relaxation were considered. The calculations were performed using the C rystal 98 code, the molecular statics method and the embedded cluster technique based on the Johnsons scattered wave method.

First-principles calculations of the electronic structure and plastic properties of CsCl, CsBr, and CsI crystals

The electronic structure and plastic properties are investigated for a number of alkali halide crystals (CsCl, CsBr, CsI). First-principles calculations are carried out within the Hartree-Fock and density-functional theory approximations using several variants of the exchange-correlation functional, including the hybrid exchange technique. The results obtained with the use of five methods are compared with the available experimental data. The tendencies revealed in the variations in the band parameters and plastic properties of the crystals under investigation are analyzed.

Embedded Cluster Calculations of the Electron Structure of the Ce3+ Impurity in Lu2SiO5 Crystals with Allowance for Crystal Lattice Relaxation and Polarization

We present results of an investigation of the electron structure of the Ce 3+ impurity in the Lu 2 SiO 5 crystal with allowance for lattice polarization and relaxation. The calculations were performed by invoking an embedded cluster technique based on a synthesis of the scattered wave method and the molecular statics method. A discussion is provided of the effect that the amount of defect-produced lattice distortion has on calculation results.

First-principles calculations of the electronic and spatial structures of the Ba1−xLaxF2+x system within the supercell model

The electronic and spatial structures of the La impurity in BaF2 are investigated using the ab initio method of linear combinations of atomic orbitals based on the Hartree-Fock approximation in the supercell model. Calculations are performed using the CRYSTAL-98 software package. Possible models of defects are discussed. The MOLSTAT computer code is employed to estimate the energies of formation of defects and their parameters. The influence of defects on the BaF2 band structure is analyzed.

Molecular-statics simulation of the cerium impurity in LSO crystals

A model is proposed for the Lu2SiO5 crystal with cerium impurity, and the defect formation energy, ion relaxation energy, and the defect-induced changes of the Madelung potentials are calculated. The calculations show substitution of the cerium ion for the lutetium ion in the Lu1 position to be energetically preferred.

Embedded cluster calculation of the Ce3+ impurity in Lu2SiO5 crystals including crystal lattice relaxation and polarization

Results of electronic structure studies of the Ce3+ impurity in Lu2SiO5 crystals allowing for lattice polarization and relaxation are given. The calculations were performed by the embedded cluster method combining the scattered wave and molecular static methods. The effect of lattice deformation induced by the defect on the results of calculations is discussed.

Self-trapped exciton configurations in Beryllium Oxide

The modern radiation technology, nuclear engineering, non-linear optics are associated with radiation-resistant optical material study. Evolution of electronic excitations in these materials is a complex multichannel process which currently has no integrated model. A special role belongs to the low-symmetry single crystals, such as beryllium oxide (BeO). We present theoretical results that advance our understanding of exciton-based channel of electronic excitations relaxation. The four possible self-trapped exciton (STE) configurations in beryllia single crystal have been investigated by using a quantum mechanical approach (Hartree-Fock and B3LYP HF-DFT hybrid functional, as implemented in the CRYSTAL09 code). B3LYP DFT functional with 30% of exact exchange was used (B3LYP30). All calculations were performed using periodic boundary conditions and full SC geometry relaxation. The lattice distortion and charge density distribution for considered defect configurations were obtained. STE-A1 luminescence energy was found to be 6.0 eV for HF and 6.5 eV for B3LYP30; STE-A2 luminescence energy was found to be 9.2 eV for HF and 7.8 eV for B3LYP30. STE-B1 luminescence energy was found to be 5.5 eV for HF, 6.2 eV for B3LYP30; STE-B2 luminescence energy was found to be 4.7 eV for HF.

On the 2s-like relaxed excited state of the F center in alkali halide crystals

The energy and spectroscopic characteristics of the first excited 2s-like electron state of the F center are presented according to the calculations performed in the framework of the variational model proposed by Gourary and Adrian. The relaxation of the crystal lattice in the vicinity of the excited F center is described. The problem of the spatial propagation of the F center is discussed. The results obtained for the 2p and 2s states of the F center are compared with each other and with the relevant experimental data.