Papers by Author: N. Novaković

Abstract: Effects induced by uniaxial compression and external electric field in P2P to P6P oligophenylene molecules are investigated by versatile calculations. In this way some useful relations between particular values of compression or field directions and intensities to specific changes in molecular structure and properties have been established, enabling estimation of possibilities for tuning the materials characteristics and their spectroscopic analyses. The results are compared to the existing experimental data and similar calculations, and some consequences for applications of oligophenylenes-based materials are discussed.

Abstract: Magnesium based composites MgH2 + X (X=Ti, Co) were synthesized by ball milling in an argon atmosphere using stainless steel vial and balls. The crystallographic behavior of the resulting powders was examined by XRD. Thermal stability and hydrogen desorption properties were investigated by thermal analysis methods. In order to obtain a deeper insight into bonding mechanisms of the transition metal in MgH2 relaxed structure, ab initio electronic structure calculation of MgH2 + X (X=Ti, Co) was performed using Full Potential Linearized Augmented Plane Wave method, implemented in WIEN2K code. DOS analysis, confirmed by DTA measurements, resulted in the conclusion that, in the composite, in comparison to MgH2, the bonding Mg-H was weakened, on account of the shortening of interatomic distances hydrogentransition metal.

Abstract: Using semi-empirical quantum mechanic (AM1, ZINDO/S) and ab-initio Hartree-Fock (HF) calculations we investigated selected structural, electronic and vibrational properties of phenylene-based oligomers from biphenyl P2P to para-sexiphenil P6P. Special attention is paid to the interplay of electrostatic and conjugation effects on torsion barrier, energy gap, charge distribution and selected vibrational modes, and their dependence on torsion angle and oligomer size.

Abstract: The structural and geometric properties of small Mo clusters are studied by means of first principles density functional theory (DFT) calculations with planewaves and pseudopotentials. The lowest energy structures of Mon (n=2-6) clusters are determined. The evolution of electronic properties with increasing cluster size is discussed. The geometric structure, average bond lengths, and binding energies of the lowest energy isomers are reported and the results are compared with the available experimental and theoretical data.

Abstract: Despite the fact that the magnetic properties of the intermetallic compounds with C15- type Laves phase structure have so far been studied intensively, the nature of magnetism in some of them is still a matter of controversy. In order to establish and understand the magnetism in the HfCo2 Laves phase with C15 (MgCu2-type) structure, calculations using FP-LAPW WIEN 97 program package for non-polarized and spin-polarized cases were made. They have shown that the spin-polarized case is more stable, i. e. the energy of its ground state is lower by about 0.15 eV. This is in collision with the measured TDPAC spectra, which show no sign of magnetic interaction, as well as with the earlier reported magnetization and susceptibility measurements, which claim that HfCo2 is Pauli paramagnet. Probable explanation for the obtained contradiction is the deviation of the real structure from the ideal one.