Some photoelectric properties of the nucleic acid bases in thin layers

The current-voltage characteristics of dark-conductivity and photoconductivity, the lux-ampere characteristics, the spectral dependence of photoconductivity and the relative quantum efficiency of vacuum deposited layers of adenine, thymine, uracil and cytosine were investigated at room temperature. The following values of photoconductivity thresholdE _th were obtained: 3·81 ±± 0·1 eV for adenine; 3·69±0·1 eV for thymine; 3·80±0·1 eV for uracil; 3·77 ± 0·1 eV for cytosine.It may be shown thatE _th is most probably the threshold value for intrinsic photoconductivity of NA bases and, consequently, corresponds to the first electron conductivity levelE _c or at leastE _c >E_th. The possible energy diagram of the NA bases is evaluated.     

Investigation of the tautomerism of nucleic acid bases by electronic-vibrational spectroscopy

Some problems on the tautomerism of nucleic acid bases have been studied by theoretical vibronic spectroscopy. Structural-dynamic models of molecules in excited states have been constructed. Based on the analysis of the change in the geometry of a pair of nucleic bases (adenine-thymine) upon electronic excitation, one possible reason for the formation of rare tautomeric forms is considered. The vibrational structure of the absorption spectra of purine and adenine tautomers has been calculated. The possibility of identifying the tautomeric forms of purine and adenine for different phase states with the aid of electronic-vibrational spectra is shown.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 703–711, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Electron-electron correlations in the model of mobile electron shells

A variational method is proposed that allows one to take into account electron-electron correlations. The variational parameters are the coordinates of the center of a one-particle atomic orbital. The displacement introduced in this way also makes it possible to graphically describe the redistribution of the electron density under an anisotropic external action in terms of a finite initial basis. A generalization of the traditional MO-LCAO scheme in the framework of the model proposed is considered.     

Generalized shells in nuclei: Hartree-Fock calculations for bubble nuclei

Hartree-Fock calculations in the bubble degree of freedom have been performed on a variety of spherical nuclei. Of particular importance are incipient bubble configurations in ³⁶Ar, ⁶⁸Se, ⁸⁴Se, ¹⁰⁰Sn, ¹¹⁶Ce, ¹³⁸Ce and ²⁰⁰Hg, each of which possesses a binding energy which is comparable to that of the normal spherical closed-shell configuration. The densities of the above nuclei display strong deviations from a uniform shape, and give rise to depletions in the nuclear interior. These nonuniformities are due both to the absence of low angular momentum states in otherwise normally occupied spherical shells, and also to strong self-consistency effects. The nonuniformities in the mass density are further enhanced for nuclei whose neutron and proton densities have depressions or peaks at approximately the same distance from the center of the nucleus. A depression of the central density is most pronounced in the nuclei ³⁶Ar, ¹³⁸Ce and ²⁰⁰Hg. Interior depletions of the density are associated with the relatively higher energies of low angular momentum single-particle levels as compared to high angular momentum single-particle levels. This effect can give rise to moderately large gaps at the Fermi surface. Finally, it is shown that in a bubble configuration, the spin-orbit splitting of low lying doublets is sometimes reversed, and that this effect is especially pronounced for levels with low angular momentum.     

Cubic-Grid Gaussian Basis Sets for electron scattering calculations Part V. Tests for simple empirical potentials

The recently developed Cubic-Grid Gaussian Basis Sets (CGGBS) are used to describe elastic scattering of low energy electrons on simple empirical potentials. The aim is to show, that the idea of constructing CGGBS by means of the best plane-wave fitting is profitable in cases in which the first Born approximation is a good starting point. We have calculated the angular dependence of the differential cross section by solving of the Lippmann-Schwinger equation for scattering on three different potentials: Exponential (V= e^–), Gaussian , and Yukawa (V= e^–/) potential. The results are compared with the exact data obtained by a direct numerical solution of the Lippmann-Schwinger equation.This work was supported by a grant No. 93018 from the U.S. — Czechoslovak Science and Technology Program, and by a grant No. 203/93/0044 of the Grant Agency of the Czech Republic.     

Multiparticle interatiomic interaction potentials for alloys using the model electron density functional method

A method for calculating multiparticle interatomic interaction potentials for binary alloys within the framework of a model electron density functional is presented. An expression for the total ground state energy of metals and alloys is obtained. It is shown that in simplicity of the computational scheme and speed of computation, this approach does not yield to the method of inserted atoms, but has a more rigorous physical basis in comparison with the latter.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 90–99, April, 1996.     

Valence transition behavior of the doped Falicov-Kimball model at nonzero temperatures

The extrapolation of small-cluster exact-diagonalization calculations is used to study the influence of doping on valence transitions in the spinless Falicov-Kimball model at nonzero temperatures. Two types of doping are examined, and namely, the substitution of rare-earth ions by nonmagnetic ions that introduce (i) one or (ii) none additional electron (per nonmagnetic ion) into the conduction band. It is found that the first type of substitution increases the average f-state occupancy of rare-earth ions, whereas the second type of substitution has the opposite effect. The results obtained are used to describe valence transition behavior of samarium in the hexaboride solid solutions Sm_1−xM_xB₆ (M=Y³⁺, La³⁺, Sr²⁺, Yb²⁺) and a very good agreement of theoretical and experimental results is found.     

Three-nucleon calculations for local potentials with the quasiparticle method

The three-nucleon system for energies below the breakup threshold is investigated with the help of the quasiparticle method. Two types of local potentials are used, namely purely attractive Yukawa potentials and the soft-core potentials of Malfliet and Tjon. The results obtained are compared with those of other calculations employing different methods.Presented at the symposium Theory of lightest nuclei, Liblice, Czechoslovakia, May 1974.     

Fluorescence spectra of some cross-conjugate ketones: Experiment and calculations based on the model of two-well adiabatic potentials

Fluorescent properties of some cross-conjugate ketones were studied at 4.2, 77, and 300 K. Anomalies were observed in the fluorescence and fluorescence-excitation spectra of one of the studied compounds; these anomalies consisted in a pronounced upset of mirror symmetry of the spectra and a large Stokes shift. The experimental spectra and the spectra calculated theoretically using the theory of two-well adiabatic potentials were subjected to a comparative analysis.     

Dynamic exchange-correlation potentials for the 2D electron gas

Recent progress in the formulation of a fully dynamical local approximation to time-dependent density functional theory (TD-DFT) appeals to the longitudinal and transverse components of the long-wavelength exchange and correlation kernel in the homogeneous electron gas, . We extend to the two-dimensional longitudinal and transverse case our work on the 3D [J. Phys.: Condens. Matter 9 (1997) 475], which accounts for two-pair excitations through an approximate decoupling of the equation of motion for the current–current response function. We present numerical results and compare with asymptotic behaviours and previous approximations.     

Approximate calculations for the two-dimensional Ising model

A self-consistent molecular field approximation for the two-dimensional, square-lattice Ising model is used to calculate the energy and magnetization. Agreement with the exact calculations is good except near the critical temperature, which differs from the exact critical temperature by 4%. The specific heat has no anomalous behavior asT approachesT _c from above, and the magnetization follows the incorrect Weiss (T _c-T)^1/2 law asT approachesT _c from below.     

The interacting boson model: Microscopic calculations for the mercury isotopes

Microscopic calculations of the parameters of the proton-neutron interacting boson model (IBM-2) appropriate to the even Hg isotopes are reported. The calculations are based on the Otsuka-Armia-Iachello boson mapping procedure, which is briefly reviewed. Renormalization of the parameters due to exclusion of the l=4 g boson is treated perturbatively. The calculations employ a semi-realistic shell-model Hamiltonian with no adjustable parameters. The calculated parameters of the IBM-2 Hamiltonian are used to generate energy spectra and electromagnetic transition probabilities, which are compared with experimental data and with the result of phenomenological fits. The overall agreement is reasonable with some notable exceptions, which are discussed. Particular attention is focused on the parameters of the Majorana interaction and on the F-spin character of low-lying levels.     

Ionization of atomic hydrogen by electron impact. Numerical calculations for the “free-fall” atomic model

The atomic model of the zero-angular momentum electron trajectory was used in numerical classical three-body calculations of hydrogen atom ionization by electron impact. The results are compared with the results for microcanonical model and with experimental data.