Calculations for antiferrodistortive phase of SrTiO3 perovskite: hybrid density functional study

The electronic and atomic structure of SrTiO3 crystals below the antiferrodistortive phase transition observed at 105 K is calculated using the hybrid B3PW functional as implemented in the ab initio CRYSTAL-2003 computer code. Such a combination of non-local exchange and correlation permits the calculation for the first time of the TiO6 octahedron rotational angle and the ratio c/a of tetragonal lattice constants in excellent agreement with experimental data. The level splitting of the bottom of the conduction band is found to be very small, <1 meV. The predicted phase-transition induced change of the optical gap from indirect to direct is confirmed by experimental photoconductivity data

Ab initio Calculations for SrTiO_3 (100) Surface Structure

Results of detailed calculations for SrTiO_3 (100) surface relaxation and the electronic structure for the two different terminations (SrO and TiO_2) are discussed. These are based on ab initio Hartree-Fock (HF) method with electron correlation corrections and Density Functional Theory (DFT) with different exchange-correlation functionals, including hybrid (B3PW, B3LYP) exchange techniques. Results are compared with previous ab initio plane wave LDA calculations. All methods agree well on both surface energies and on atomic displacements. Considerable increase of Ti[Single Bond]O chemical bond covalency nearby the surface is predicted, along with a gap reduction, especially for the TiO_2 termination

The first-principles treatment of the electron-correlation and spin-orbital effects in uranium mononitride nuclear fuels

The DFT+U calculations were employed in a detailed study of the strong electron correlation effects in promising nuclear fuel -- uranium mononitride (UN). A simple method for solving the multiple minima problem in DFT+U simulations and insure obtaining the correct ground state is suggested and applied. The crucial role of spin-orbit interactions in reproduction of the U atom total magnetic moment is demonstrated. Basic material properties (the lattice constants, the spin- and total magnetic moments on U atoms, magnetic ordering, and the density of states) were calculated varying the Hubbard U-parameter. Varying the tetragonal unit cell distortion, the meta-stable states have been carefully identified and analyzed. The difference of the magnetic and structural properties obtained for the meta-stable and ground states are discussed. The optimal effective Hubbard parameter Ueff =1.85 eV reproduces correctly the UN anti-ferromagnetic ordering, and only slightly overestimates the experimental total magnetic moment of U atom and the unit cell volume.JRC.E.3-Materials researc

Computer Modeling of Point Defects, Impurity Self-Ordering Effects and Surfaces in Advanced Perovskite Ferroelectrics

The calculated optical properties of basic point defects - F-type centers and hole polarons - in KNbO_3 perovskite crystals are used for the interpretation of available experimental data. The results of quantum chemical calculations for perovskite KNb_xTa_(1-x)O_3 solid solutions are presented for x=0, 0.125, 0.25, 0.75, and 1. An analysis of the optimized atomic and electronic structure clearly demonstrates that several nearest Nb atoms substituting for Ta in KTaO_3 - unlike Ta impurities in KNbO_3 - reveal a self-ordering effect, which probably triggers the ferroelectricity observed in KNb_xTa_(1-x)O_3. Lastly, the (110) surface relaxations are calculated for SrTiO_3 and BaTiO_3 perovskites. The positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized using the classical shell model. Strong surface rumpling and surface-induced dipole moments perpendicular to the surface are predicted for both the O-terminated and Ti-terminated surfaces

Методические аспекты определения предполагаемой (предельной) стоимости объектов при реализации проектов на базе СЗПК

The paper is devoted to the study of the issues of determining the estimated (marginal) cost of investment projects that are implemented within the framework of the IPA. The purpose of the study is to develop scientific and practical recommendations for determining the estimated (marginal) value of real estate objects created in the framework of investment projects implemented on the basis of the IPA. The paper is relevant because current regulatory documentation does not clearly define the concepts of estimated (marginal) cost of infrastructure objects, and there are no recommendations for their assessment, which leads to distortions of the cost base for obtaining subsidies and impacts the evaluation of the effectiveness of such projects. The scientific novelty of the research consists in the development of scientific and practical recommendations for determining the estimated (marginal) value of real estate objects created as part of an investment project implemented on the basis of the IPA. The authors used the following methods of scientific research: deduction, induction and logical method. The concept of the estimated (marginal) value of real estate objects is clarified, which is based on the estimated cost of construction, taking into account a certain number of assumptions. A review of the current methods of calculating the estimated value in Russia and abroad is conducted. It is concluded that in Russia there is no single base for determining the cost of the CIW. The basic index method in the prices of 2000– 2001 significantly reduces the accuracy of calculations. The idea of forming a new dynamic system of the resource-index method, which takes into account the life cycle of a building and is based on big data of price information in construction, on the basis of which it is possible to develop a system of forecasting the estimated value of an object using machine learning methods, is prospective.Статья посвящена исследованию вопросов определения предполагаемой (предельной) стоимости инвестиционных проектов, которые реализуются в рамках соглашения о защите и поощрении капитальных вложений (СЗПК). Цель исследования — разработка научно-практических рекомендаций по определению предполагаемой (предельной) стоимости объектов недвижимости, созданных в рамках инвестиционных проектов, реализуемых на базе СЗПК. Актуальность работы состоит в том, что в действующей нормативной документации не четко определены понятия предполагаемой (предельной) стоимости объектов инфраструктуры, отсутствуют рекомендации по ее оценке, что приводит к искажениям стоимостной базы для получения субсидий и отражается на оценке эффективности таких проектов. Научная новизна исследования состоит в разработке научно-практических рекомендаций по определению предполагаемой (предельной) стоимости объектов недвижимости, создаваемых в рамках инвестиционного проекта, реализуемого на базе СЗПК. Авторы использовали следующие методы научного исследования: дедукция, индукция, логический метод. Уточнено понятие предполагаемой (предельной) стоимости объектов недвижимости, в основе которой лежит сметная стоимость строительства с учетом определенного количества допущений. Проведен обзор действующих методик расчета сметной стоимости в России и за рубежом. Сделан вывод, что в России отсутствует единая база определения стоимости строительно-монтажных работ (СМР). Базисно-индексный метод в ценах 2000–2001 гг. существенно уменьшает точность расчетов. Перспективной видится идея формирования новой динамической системы ресурсного-индексного метода, которая учитывает жизненный цикл здания и базируется на больших данных ценовой информации в строительстве, на основе которых возможно разработать систему прогнозирования сметной стоимости объекта методами машинного обучения

First principles and semi-empirical calculations of atomic and electronic structure for the (100) and (110) perovskite surfaces

We present and discuss results of the calculations for BaTiO_3 and SrTiO_3 surface relaxation with different terminations using a semi-empirical shell model (SM) as well as ab initio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) formalisms. Using the SM, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized. This permits us determination of surface rumpling and surface-induced dipole moments (polarization) for different terminations of the (100) and (110) surfaces. We also compare results of the ab initio calculations based on both HF with the DFT-type electron correlation corrections, several DFT with different exchange-correlation functionals, and hybrid exchange techniques. Our SM results for the (100) surfaces are in a good agreement with both our ab initio calculations and LEED experiments. For the (110) surfaces O-termination is predicted to be the lowest in energy