No abstract

No abstract

The atomic structure and mechanical properties of the carbyne (monatomic linear chains), containing from 2 to 21 carbon atoms, are theoretically investigated by ab-initio methods. We demonstrate the existence of a stable cumulene-structure in the inner part of chains with the number of atoms N>=10. We present a general stress-strain diagram of chains until the moment when they break, which enables to determine their strength, elasticity and fragility. For chains with N>=4, the relationship between the strength of the chain and the binding energy of the edge atom in the chain is established. The existence of scale-effect and "even-odd" effect for such properties as strength, elasticity and fragility is observed. We demonstrate that the 5-atom carbon chains show the maximum strength value.Comment: 8 pages, figure

The results of the high-field technique for obtaining and testing the carbyne strength in situ are presented. By using molecular dynamics simulation and ab initio calculations, a comprehensive analysis of the results is executed. High-field technique for experimental measurement of the carbyne strength in situ is briefly described. It is shown that the technique used gives a lower estimation for strength of carbyne, which equals 251 GPa at T = 77 K. This value is close to the strength 7.85 nN (250 GPa) of contact atomic bond between carbyne and graphene sheet, from which the monatomic chain is pulled. The strength of carbyne itself is determined by strength of an edge atomic bond and it is ≈ 12.35 nN (393 GPa) at T = 0 K. For carbynes containing more than 10 to 12 atoms, the coefficient of elasticity (kY = 145.40 nN) and the elastic modulus (Y = 4631 GPa) are ascertain.

No abstract

Abstract. Carbon and nitrogen austenites, modeled by Fe 8 N and Fe 8 C superstructures are studied by full-potential LAPW method. Structure parameters, electronic and magnetic properties as well as hyperfine interaction parameters are obtained. Calculations prove that Fe-C austenite can be successfully modeled by ordered Fe 8 C superstructure. The results show that chemical Fe-C bond in Fe 8 C has higher covalent part than in Fe 8 N. Detailed analysis of electric field gradient formation for both systems is performed. The calculation of electric field gradient allow us to carry out a good interpretation of Mössbauer spectra for Fe-C and Fe-N systems.

The electronic structure of ATiO, (A = Ca, Sr, Ba) titanates is studied by the APW and X,-SW methods. The degree of participation of atom A states in formation of the valence band and the conduction bandis shown to grow in this order. The results are confirmed by X-ray emission and XPS experimental data. The peculiarity of the electronic structure of BaTiO, is the presence of Ba 5p, 5d, 4f levels in the vicinity of the valence band and the bottom of the conduction band.Due to this fact in the investigated series of the compounds the Ti-0 interaction is weakened in BaTiO,.(A = Ca, Sr, Ba

Iron nitride Fe 4 N is studied by full-potential LAPW method. Structure parameters, electronic and magnetic properties as well as hyperfine interaction parameters are obtained. We observe perfect agreement with experimental results. Hypothetical Fe 4 N structure was also calculated to study the influence of disordering effects on parameters of Mössbauer spectra. We performed detailed analysis of EFG formation on Fe nuclei including magnetization effects. We show that the formation of N-Fe-N local configuration is energetically favourable in nitrogen austenites.