Fatima U. Abuova

A classical molecular dynamics simulation of cation diffusion in isolated crystals (U_xPu_yTh_1−x−y)O₂ bounded by a free surface was performed. It was shown that in the bulk of the same model crystallite, the diffusion coefficients of cations of all types were practically identical. At the same time, the cation diffusion coefficients changed with the melting temperature of nanocrystals, which increased with increasing thorium content. At a given temperature, the diffusion coefficients were the higher, the lower were the melting points of the (U_xPu_yTh_1−x−y)O₂ crystallites. The temperature dependences of the diffusion coefficients in crystallites of different compositions converged when using coordinates normalized to the melting points.

Classical molecular dynamics simulation of cation diffusion in isolated crystals (UxPuyTh1xy)O2 bounded by a free surface was performed. It was shown that in the bulk of the same model crystallite the diffusion coefficients of cations of all types were practically identical. At the same time, the cation diffusion coefficients changed with the melting temperature of nanocrystals, which increased with increasing thorium content. At a given temperature, the diffusion coefficients were the higher, the lower were the melting points of the (UxPuyTh1xy)O2 crystallites. The temperature dependences of the diffusion coefficients in crystallites of different compositions converged when using coordinates normalized to the melting points.

The optical properties of the tetragonal phase of BaTiO ₃ have been studied using density functional methods, applying the generalized gradient approximation at room temperature and a hybrid functional for static lattice analysis.

This research investigates the structural, electronic, mechanical, and vibrational properties of double half-Heusler compounds with the generic formula Ti2Pt2ZSb (Z = Al, Ga, and In) using density functional theory calculations. The generalized gradient approximation within the Perdew-Burke-Ernzerhof functional was employed for structural optimization and the hybrid HSE06 functional for electronic properties. Our results demonstrate that these compounds are energetically favorable, dynamically and mechanically stable. Electronic structure calculations reveal that Ti2Pt2AlSb double half-Heusler compound is a non-magnetic semiconductor with an indirect bandgap of 1.49 eV, while Ti2Pt2GaSb and Ti2Pt2InSb are non-magnetic semiconductors with direct bandgaps of 1.40 eV. The alloys exhibit low lattice thermal conductivity (2.35–2.66 W/mK) and high melting temperature (1211–1248 K), making them promising candidates for high-technological applications. Further performed analysis, including phonon dispersion curves, electron localization function (ELF), and Bader charge analysis, provides insights into the bonding character and vibrational properties of these materials.

В данной статье исследуются упругие свойства кристалла Na₂SO₄ (тенардит, орторомбическая фаза V, группа симметрии FDDD) с примесями методом функционала плотности (DFT) с использованием гибридного функционала HSE06. Основная цель работы — изучение механических характеристик Na₂SO₄ под воздействием различных давлений с акцентом на разработку более эффективных термолюминесцентных дозиметров (ТЛД). Проведённое моделирование позволяет лучше понять, как структурные изменения в кристалле под давлением влияют на его упругость и пластичность. Важным достижением является выявление критических точек при давлении около 12 ГПа, где происходит переход материала из пластичного состояния в хрупкое. Рассмотрены основные механизмы, управляющие деформацией кристалла, а также возможность фазовых переходов, влияющих на электронные и упругие свойства. Проведено детальное сравнение полученных данных с экспериментальными значениями ширины запрещённой зоны и упругих модулей, что подтвердило адекватность расчётной модели. Эти выводы имеют важное значение для дальнейшего использования Na₂SO₄ в условиях экстремальных механических воздействий, что делает его перспективным для применения в дозиметрии радиационного излучения и других областях, где необходима высокая устойчивость материала к внешним нагрузкам.

MgF₂ with a rutile structure is important wide‐gap optical material with numerous applications. We present and discuss the results of calculations for basic hole defects – interstitial F atoms (called also the colour H centers). This study is based on the large scale ab initio DFT calculations using hybrid B3PW exchange‐correlation functional as implemented into CRYSTAL computer code. The electronic structure, atomic geometry, charge density distribution are calculated and compared with similar defects in CaF₂ fluorite. It is shown that the H centers oriented nearly parallel to the (110) axis are energetically more favourable than those oriented along the (001) axis, in agreement with experiment.